Jury selection in the trial of John W. Hinckley Jr. moved behind closed doors yesterday and, by late afternoon, court officials said that 22 prospective jurors had been tentatively qualified to hear the case of the man accused of trying to assassinate President Reagan.

Another 10 prospective jurors were excused from service.

Hinckley's trial formally began Tuesday morning, and since then the judge and lawyers in the case have been consumed with the painstaking process of screening a pool of 90 prospective jurors, 12 of whom will eventually make up the jury.

U.S. District Judge Barrington D. Parker indicated yesterday that actual selection of the 12 jurors and six alternates will commence once the court has come up with a pool of about 48 eligible jurors.

The selection process resumed shortly after 9 a.m. yesterday with the prosecution and defense lawyers huddled around the judge's bench where jury pool members were questioned in private about their knowledge of the case and their opinions about mental illness and psychiatry.

Hinckley, who contends he was mentally ill when he attacked the president and thus was not criminally responsible for his acts, was present when the court session opened in the large ceremonial courtroom, sitting alone at the defense table surrounded by deputy U.S. marshals. He appeared more animated than he had been at the first day of trial, paging through a document and gazing around at the portraits of various judges above him.

Behind Hinckley sat the pool of prospective jurors, some of whom were reading paperback books and magazines as they waited for their turn to come to the bench. As the morning wore on, Parker decided to move the questioning session to a small conference area behind the courtroom. Hinckley, by then visibly restless, returned to his cell in the courthouse basement, and the majority of the prospective jurors, clearly eager for more comfortable surroundings, were permitted to wait in the jurors' lounge.

For the rest of the day, the heavily secured courtroom was virtually empty but for a contingent of deputy marshals, a few spectators, a handful of jury pool members ready to be questioned, and a small group of news reporters and sketch artists.

One member of the jury pool, CBS White House correspondent Bill Plante, was excused from service at the outset of yesterday's court session. On Tuesday, Plante, who was not at the scene of the March 30 shooting, told Parker that he is in regular contact with the president and is a longtime friend of Press Secretary James Brady, who was also wounded.

Brady, who was shot in the head and suffered lasting injuries, was not on the list of potential prosecution witnesses that was read to the jury pool Tuesday. However, Brady's wife, Sarah, told UPI yesterday that Brady was willing to testify and had been contacted by prosecutors but heard nothing further from them.

The Justice Department said last night that "in light of all the evidence which we are in a position to present to the jury, we have elected not to subject Mr. Brady to reliving the tragedy through the trial."

Two other persons injured during the shooting, retired D.C. police officer Thomas Delahanty and U.S. Secret Service agent Timothy McCarthy were on the government's witness list.

Assistant U.S. Attorney Roger M. Adelman told the prospective jurors that Reagan might testify at the trial.

Even though none of the prospective jurors has actually been selected for Hinckley's trial, Parker warned them yesterday that they must nevertheless avoid watching or listening to any comment about the case on radio or television.

"Turn a deaf ear, close your eyes, close your ears," Parker told the jurors, after noting that he had forgotten to give them that admonishment before they left the courthouse Tuesday.

Parker also told them to "shun" newspaper accounts of the trial.

"I can't be too emphatic. I can't be too strong in asking you to do that," Parker said.

The laborious jury screening process is scheduled to start up again at 9 a.m. today. The actual questions addressed to the jurors in private session have not been disclosed, and the court record of the proceedings has been sealed. But both the prosecution and the defense proposed asking many questions involving the jurors' own experience with the sensitive issue of mental illness.

For example, both sides requested that Parker ask the jurors if they, or any members of their family, have undergone psychiatric or psychological treatment. Hinckley's lawyers also wanted to ask the jurors if they, or any of their relatives or friends, had ever atttempted suicide or whether they had an opinion about such an act. Hinckley has twice attempted sucide since his arrest.