This appeal presents the sole issue of whether the trial court erred by refusing to allow the defendant to withdraw his guilty plea prior to sentencing where it was alleged that the defendant and his attorney were mistaken as to the true nature of the plea bargain to which the defendant had agreed.
On March 7,1980, the defendant, David Lasher, was arrested by a state police undercover unit of the Statewide Narcotics Task Force for conspiracy to sell marijuana in violation of General Statutes § 53a-48 and possession of a weapon in a motor vehicle in violation of General Statutes § 29-38.
On March 8, 1980, the defendant appeared in court and was advised of his rights before plea. More than a year later, on March 10, 1981, as a result of plea bargaining, the defendant agreed to plead guilty to the charge of conspiracy to sell marijuana.1 During the plea *261proceeding, the court inquired into the factual basis of the plea, and explained to the defendant that he was giving up his right against self-incrimination and his rights to confrontation and trial. The court further indicated the penalty for the offense charged and warned the defendant that the court was not bound by the state’s recommendation. Additionally, the court inquired into the voluntariness of the plea and whether the defendant was under the influence of drugs or *262otherwise incompetent during the plea proceeding. The court found that there was a factual basis for the plea and that the plea was voluntary. Thereafter, the court entered a finding of guilty, ordered a presentence investigation and continued the case for sentencing.
The defendant’s attorney again appeared before the court on May 22, 1981. At that time he informed the court that a dispute had arisen between himself and the state’s attorney as to the terms of the presentence recommendation stated at the March 10, 1981 pro*263ceeding. The court, therefore, granted counsel a one week extension to review the transcripts of the guilty plea.
The defendant was present for sentencing on May 29, 1981. On that date, prior to the imposition of sentence, the defendant’s counsel, alleging that the terms of the plea agreement as they appeared in the March 10, 1981 transcript were materially different from what he had explained to the defendant, moved to withdraw the guilty plea.2 The defendant’s counsel at no time offered any testimony in support of his mo*264tion to withdraw the plea. The court, after hearing argument and reviewing the March 10,1981 transcript, denied the defendant’s motion. The court also denied the defendant’s motion that he be committed to the “TASC”3 drug dependency program and imposed a sentence of one and one-half to three years to serve. A nolle was entered on the weapons in a motor vehicle charge.
On appeal the defendant asserts that he should be allowed to withdraw his guilty plea on the basis of Practice Book § 721 (2). That section authorizes the withdrawal of a guilty plea upon proof that “[t]he plea was involuntary, or it was entered without knowledge of the nature of the charge or without knowledge that the sentence actually imposed could be imposed.” The defendant claims that the record at the time of the plea (as set out in footnote 1) indicates that both the defendant and his attorney believed that, as part of the bargain, the defendant would be committed to the commissioner of mental health pursuant to General Statutes § 19-485 (now General Statutes § 21a-285) to allow him to continue participating in the “TASC” drug dependency program, with the sentence imposed suspended for the duration of the program, in return for his guilty plea. The defendant insists that this mistake of fact on the part of the defendant and his *265attorney as to the terms of the plea agreement persisted despite the statement by the assistant state’s attorney of his intention to (1) recommend a sentence of not less than two and one-half years and not more than five years; (2) not to prosecute on a second count; and (3) not to oppose the defendant’s application for drug dependency treatment.
In essence, the defendant claims that this guilty plea was not voluntary and intelligent because both the defendant and his attorney were laboring under a subjective misunderstanding of the plea agreement.4 It is to be underscored that the defendant does not allege a broken prosecutorial promise. See Santobello v. New York, 404 U.S. 257, 92 S. Ct. 495, 30 L. Ed. 2d 427 (1971).
In order for a plea of guilty to be constitutionally valid, the record must affirmatively disclose that the defendant entered the plea voluntarily and intelligently. Boykin v. Alabama, 395 U.S. 238, 242, 89 S. Ct. 1709, 23 L. Ed. 2d 274 (1969); State v. Godek, 182 Conn. 353, 356, 438 A.2d 114 (1980), cert. denied, 450 U.S. 1031, 101 S. Ct. 1741, 68 L. Ed. 2d 226 (1981).
“Before a guilty plea is accepted a defendant may withdraw it as a matter of right. Practice Book, 1978, § 720. After a guilty plea is accepted but before the imposition of sentence the court is obligated to permit withdrawal upon proof of one of the grounds in § 721. An evidentiary hearing is not required if the record of the plea proceeding and other information in the court file conclusively establishes that the motion is without merit. See Fontaine v. United States, 411 U.S. 213, 215, *26693 S. Ct. 1461, 36 L. Ed. 2d 169 (1973).” (Footnote omitted.) State v. Torres, 182 Conn. 176, 185, 438 A.2d 46 (1980).
The burden is always on the defendant to show a plausible reason for the withdrawal of a plea of guilty. Blue v. Robinson, 173 Conn. 360, 374, 377 A.2d 1108 (1977); State v. Slater, 169 Conn. 38, 46, 362 A.2d 499 (1975). In considering whether to hold an evidentiary hearing on a motion to withdraw a guilty plea the court may disregard any allegations of fact, whether contained in the motion or made in an offer of proof, which are either conclusory, vague or oblique. State v. Torres, supra, 185. Such allegations are discountenanced. State v. Deboben, 187 Conn. 469, 474, 446 A.2d 828 (1982). To warrant consideration, the defendant must allege and provide facts which justify permitting him to withdraw his plea under § 721.5 Id.
An examination of the record of the March 10,1981 guilty plea reveals that the court personally addressed the defendant and explained to him the penalties for the crime charged. The court explained to the defendant that he had the right to confront witnesses against *267him, the right to trial and the right to avoid self-incrimination. The defendant responded affirmatively when he was asked if he understood and wished to give up these rights. The court questioned the defendant about the voluntariness of his plea. The defendant indicated that the plea was voluntary. The court further inquired as to the factual basis of the plea and the defendant admitted being part of the drug transaction. At the close of the canvass the court found that the plea was voluntary with a factual basis and thus entered a finding of guilty. These conclusions must stand unless they are legally and logically inconsistent with the facts found. Pandolphe’s Auto Parts, Inc. v. Manchester, 181 Conn. 217, 221, 435 A.2d 24 (1980); see State v. Slater, supra, 45-46. Here we cannot make such a finding.
Defense counsel, in support of his oral motion to withdraw the guilty plea, offered nothing other than the conclusory statement that the plea agreement as it appeared in the March 10 transcript was “somewhat materially different” than what he had explained to the defendant. The defendant was present, yet his testimony as to what defense counsel had related to him was not presented to the court. Indeed, defense counsel did not request an evidentiary hearing or make an offer of proof. The defendant’s unsupported conclusory claims in light of our statements in Torres and Deboben, supra, cannot, in the presence of a facially valid plea of guilty, serve as sufficient proof to obligate the withdrawal of the defendant’s plea.
The question that remains is whether the defendant should now be afforded an opportunity, through a belated evidentiary hearing, to make a factual showing that he failed to understand that the sentence actually imposed would be or could be imposed. This record furnishes some basis for such an inquiry, since the colloquy at the time of the taking of the plea, on *268March 10, 1981, disclosed that the defendant’s attorney and the state’s attorney differed in their understanding of the terms of the plea bargain. Usually it is appropriate to infer that defense counsel, having been asked by the court to explain a proposed plea bargain to the defendant, will do so accurately. Such an inference is less plausible in this case, when no one, with the possible exception of the defendant who announced his confusion, recognized that there was a problem or took steps to alleviate it. Nor is it clear, on this record, that conclusive effect should be given to the defendant’s statement, after consultation with his counsel, that he was in accord “with what the state’s attorney has just finished saying.”
We reject this route for two reasons, one relating to its lack of timeliness and the other relating to the inherent problems of proof that it would generate. In order to ascertain what uncertainties existed, either objectively or subjectively, testimony would be required from at least the attorney for the defense and arguably the state’s attorney as well. Such inquiries are better pursued, as we have held in cases concerning alleged inadequacy of counsel, by habeas corpus proceedings. State v. Mason, 186 Conn. 574, 578-79, 442 A.2d 1335 (1982).
There is no error.
In this opinion the other judges concurred.