The 29-month-long McMartin Pre-School molestation trial edged even closer to a mistrial Thursday as an ailing juror remained hospitalized with an undiagnosed illness.

Los Angeles Superior Court Judge William Pounders delayed proceedings until Sept. 11, when the juror will be replaced by the last remaining alternate if he is unable to rejoin the panel. The judge said little time will be lost by the delay, since the court was scheduled to be in session only three days next week and the attorneys can use the down time to work on their closing arguments.

Pounders said the juror's physician is still awaiting the results of a battery of tests before commenting on the seriousness of his condition, which was initially thought to be a case of shingles.

Jury Has Dwindled

The marathon trial began in April, 1987, with the selection of 12 regular jurors and six alternates, and was expected to last at most one year. Now in its third year, the jury has dwindled over the months to the current 13.

One juror was dismissed for being inattentive. A second suffered back problems. A third was paralyzed by a stroke. A fourth ran into job problems. And a fifth had to undergo emergency surgery. The loss of a sixth juror, whose company folded, was averted when the judge arranged to have him put on the county payroll for the duration of the trial.

Pounders has ruminated lately about "the probability" of a mistrial, but stressed Thursday that the situation has not yet reached that stage, and that he sees no need to discuss various proposals to avert it so long as he has an intact, 12-member jury.

But he said if it becomes necessary, he "absolutely" would accept a stipulation by both sides to continue with fewer than 12 jurors, rather than declare a mistrial.

Deputy Dist. Atty. Lael Rubin was optimistic, with the trial estimated to last about two more months. "There's no reason to panic. We're not at that point yet. We still believe we'll have 12 jurors to decide this case."

Likewise, defense attorney Danny Davis, who represents Ray Buckey, said: "We're simply not there. It's premature. I'm going to do what I can to preserve all 13 (jurors) we have." He noted that he had originally proposed selecting eight alternates. Rubin told the judge that the prosecution will propose Sept. 11 that both sides stipulate a willingness to finish the trial with 11 jurors, should another have to be released between now and the time the case goes to the jury in December.