Mary Treadwell, saying she feared that the 10-day-old jury deliberations in her fraud and conspiracy case might be turning into a "sporting contest" on her life, abruptly and surprisingly told a federal judge yesterday that she wanted to plead no contest to the charges against her.

A short time later, however, after a bench conference in which Treadwell admitted no guilt and asserted that "I won my trial," U.S. District Judge John Garrett Penn rejected her offer.

Meanwhile, the jury, unaware of Treadwell's announcement, continued its marathon deliberations, again without reaching a verdict. The jury of eight women and four men has now considered the 21 conspiracy, fraud, tax evasion and false-statement charges against Treadwell for 73 1/2 hours, apparently a record length for a criminal case in federal court here.

Four hours after Treadwell made her offer, Penn ordered the 12 jurors and five alternate jurors sequestered in a hotel until a verdict is reached to make certain they do not learn of the incident. Penn told the jurors he regretted the necessity of sequestering them, but did not tell them why it was suddenly being done on the 38th day of the trial.

Treadwell's declaration came at a courtroom hearing during which she stood up suddenly and told Penn: "I would like to change my plea in this case." Her comments to Penn in the bench conference, however, showed that she was upset mostly because she felt the jury's deliberations might be centering on something other than what was contested during the 20 days of testimony.

Her no contest plea, if it had been accepted, would have had the same practical effect as if she had pleaded guilty. Each charge carries a penalty of five years' imprisonment, a $10,000 fine or both.

Treadwell is accused of using P.I. Properties Inc., her now-defunct real estate firm, to defraud the federal government and the impoverished tenants at the Clifton Terrace apartment complex, which the firm owned in the mid-1970s, of thousands of dollars to enrich herself.

During the bench conference, she seemed particularly upset that a potentially damaging prosecution document not admitted into evidence during the trial was inadvertently sent to the jurors along with about 400 government reports, bank checks, memos, notes and charts that were introduced as exhibits.

The jurors discovered the one-page document last Friday and called it to Penn's attention. The document appeared to suggest that P.I. Properties was remiss in not reporting all corporate loans to the Department of Housing and Urban Development, which sold the 285-unit Clifton Terrace project to the firm.

Penn told the jurors twice not to consider the document, but he denied a request by John W. Nields Jr., Treadwell's court-appointed attorney, that he declare a mistrial or dismiss 12 false statement charges that are related to the document.

"I do not believe that got in that room by accident," Treadwell told Penn yesterday.

"I won my trial," she said later during the 23-minute bench conference. "I'm losing the case. My suggestion is I plead at this point just where I am: no contest."

"Why are you so sure you are losing the case?" Penn asked her.

"I am so sure because whatever they are deliberating on is different than what they heard in the courtroom," Treadwell responded.

"The other thing I have a big problem with is the government keeps treating this case like it's a joke and a game, all right?" Treadwell said. "And they keep treating it like there are sporting rules. Well, it's my life and I cannot look at it from the same perspective as if it is a sporting contest, especially when if it were a sporting contest, all right, they are not quite playing it clean, but it's my life."

Penn eventually told Treadwell that "there's really no legal request for a change" in her plea from not guilty to no contest and denied the offer.

After Nields described Treadwell's anguish over the case in open court, Assistant U.S. Attorney William D. Pease sarcastically told Penn, "We sometimes wish the tenants of Clifton Terrace had the same podium to make these fine speeches that Miss Treadwell has had."

With that, Treadwell angrily slammed a notebook onto the defense table.

"Miss Treadwell, I will not tolerate any outbreaks in this courtroom from anyone," Penn admonished her.

Penn at first sealed the transcript of the bench conference he had with Treadwell but later opened it after sequestering the jury and over the objections of Pease. The prosecutor said enough had already been heard of Treadwell's "self-serving comments."