The guilty plea of Joan M. Booth, a key official of a Youth Pride Inc. spinoff company, must stand, U.S. District Court Judge John Garrett Penn ruled yesterday.

Booth had sought to "clarify" her guilty plea to conspiracy and tax evasion, saying her lawyer had not explained to her the meaning of the indictment against her before she told Penn last October: "I understand that what I did was wrong."

The indictment of Booth last year charged that she conspired with her sister Mary Treadwell, Charles W. Rinker Jr., and Robert E. Lee in an alleged scheme to steal thousands of dollars from the federally financed housing project they managed.

After first pleading not guilty to the charges, Booth pleaded guilty to two counts in the indictment last October. Last month, she sought to modify her plea, saying she denied conspiring with anyone except Lee.

In rejecting Booth's request, Penn ruled yesterday that she had been "effectively and adequately" represented by Grandison E. Hill, who was then her lawyer.

The judge recounted how Hill participated with Booth and government lawyers in working out a plea agreement that reduced the number of counts against her from 30 to two. Over a period of about a month last fall, Penn wrote, Hill discussed the case with Booth on about 10 occasions.

"The court finds that Mr. Hill negotiated the plea agreement with the best interests of his client in mind," Penn said.

"Booth is intelligent and fully understands the charges against her," Penn wrote. "Her responses to questions from the Court last October when she pleaded guilty were considered and were not made without thought."

Penn wrote, "There is no question that the plea entered by this defendant on Oct. 20 was a voluntary plea, that she understood the plea, that she understood the questions posed by the court, that she had sufficient time to consult her counsel both before and during the plea, that she was fully satisfied . . . with the representation afforded by Mr. Hill, that she understood the possible consequences of her plea, and that there was a factual basis for the plea."

Lee has pleaded guilty to some of the charges, while charges against Rinker have been dismissed at the request of the government, based in part on the results of a lie detector test. Treadwell is scheduled to stand trial May 31.

Booth had said that she entered the guilty plea in part because prosecutors had threatened to allege that she had sexual relations with government officials in an attempt to receive favorable treatment for P.I. Properties, the Youth Pride Inc. spinoff firm. But Penn wrote that while government prosecutors brought up the matter in meetings with Booth, they never used the threat of the allegation to try to influence her plea.

Thomas Abbenante, who now represents Booth, said he would have no comment until he reads the opinion.