Circuit Court Judge Percy Thornton said yesterday he "will not tolerate" a repeat of the "personal assassination and vilification" among attorneys that characterized last month's bribery trial of Alexandria prospecturo William L. Cowhig.

The comments by the Prince William County judge came in a pretrial hearing in Manassas at which Special Prosecutor Edward J. White dropped an earlier request that the impending trial of Cowhig on a gambling charge be postponed. The trial is scheduled to begin Jan. 22.

Thornton also granted a motion by White to extend the period covered by Cowhig's indictment from March 1, 1977, to Sept. 1 of that year, instead of making July 30, 1977, as the cutoff date. White has said he wanted the change "to conform to evidence in the case."

Thornton's remarks about last month's trial, in which Cowhig was acquitted, were made in a bench conference with White and defense attorney James C. Clark. Their words could be heard clearly by courtroom spectators.

"I turned the other cheek so many times (in the earlier trial) they hurt," said White, as he showed the judge a copy of a letter he said he had received that made derogatory comments about him and his ethics.

Thornton nodded and said, "I have never seen as much personal assassination and vilification as I saw" in the December trial. "I will not tolerate that in this trial."

The bribery trial, in which Cowhig was cleared of charges he had taken bribes from an Alexandria bingo game operator, was marked by unusually sharp personal exchanges between White and defense lawyers Louis Koutoulakos and Leonard B. Sussholz.

White, who did not place the letter in the court file and refused to discuss it with reporters, assured Thornton he was not referring to the conduct of Clark. Clark did not participate in Cowhig's defense last month.

Koutoulakos and Sussholz could not be reached yesterday for comment.

The two lawyers attacked the credibility of the bribery case against Cowhig by pointing out repeatedly that prosecutor White had succeeded in changing the dates of the period of the alleged bribery after the indictment had been handed down.

In the forthcoming trial, Cowhig is accused of one count of gambling for allegedly conducting an illegal bingo operation in Alexandria during 1977. He is scheduled to be tried in March on a separate gambling charge.

White said yesterday he will call 11 witnesses later this month, and denied Clark's contention that the case rests exclusively on the testimony of Robert Hinkle, a former employe of the bingo games.