John W. Hinckley Jr.'s mother, weeping as she described the last time she saw her youngest child before he shot President Reagan, told a federal jury yesterday her son had a "haunted look" and suffered "depression and total despair" in the months before the

After several unhappy years as a college student, "John just seemed to be going downhill, downhill, downhill and becoming more withdrawn, more and more antisocial, more depressed, and so down on himself," JoAnn Hinckley told the jury on the third day of testimony in her son's trial on charges of attempting to assassinate the president.

"He was just discouraged and we were just terribly worried about him . . . . We didn't know what was wrong, but we knew something was not right."

Hinckley waved as his mother walked into the courtroom wearing a salmon pink dress with a rounded collar and small bow. He smiled when she described two cats that he "adored" when he was a child and laughed when she tried to remember his boyhood friend "Yogi." He looked with annoyance at a prosecutor who objected to a part of his mother's testimony and fidgeted as she told about her frustrations because her son "had no direction in his life."

Following a psychiatrist's advice, Mrs. Hinckley said, she and her husband devised a plan requiring their son to be self-sufficient and out of the family home by March 30, 1981--the day he shot Reagan and three others outside the Washington Hilton Hotel.

"We wanted John to be self-supporting, to be a happy child, to stand on his own feet," Mrs. Hinckley said during more than four hours of testimony in her son's defense.

The plan required Hinckley to have a job by March 1 to help him end his long dependence on his parents, Mrs. Hinckley said.

"The harder we tried to push him from us, the harder he tried to stay," she said.

Hinckley was to start a job on Feb. 23, his mother testified, but while his parents were on a business trip, he left home. He left a note behind, Mrs. Hinckley said, which read: "Your prodigal son has left again to exorcise some demons."

A week later, on March 6, Mrs. Hinckley said, her son called home from New York, "almost incoherent" and pleading, "Can I come home?" The psychiatrist who had been consulting with the family and meeting with Hinckley for months--Dr. John Hopper of Evergreen, Colo.--suggested "that we just give John $100 and tell him goodbye," Mrs. Hinckley said.

"We couldn't do that," she told the jury.

His parents paid for Hinckley to fly home, but mindful of "the plan," Mrs. Hinckley said, her son was made to spend one more night on his own before he came home. In the following days, she told the jury, Hinckley occasionally came to the family home in suburban Denver to pick up books and records he was selling to support himself.

On March 25, after Hinckley called his parents and said he wanted to go to California, where he had tried before to pursue a career in music, Mrs. Hinckley drove him to the Denver airport. The long ride, she recalled, was made in silence.

"I broke the plan for the first time and I gave him some money of my own. I just couldn't stand to see him go off without any money," she told the jury.

Her son, she said, "looked so bad and so sad and so absolutely in total despair, I was frightened." But, she said, she had to stick to "the plan."

At the airport, "John got out of the car and I couldn't even look at him," Mrs. Hinckley said, her steady voice breaking with emotion.

"He said 'Well, Mom, I want to thank you for everything you've ever done for me,' " Mrs. Hinckley said.

"I said you're very welcome and I said it so coldly . . . and then I drove off and that was the last I saw of John," she said, breaking into tears.

At the defense table in the well of the courtroom, Hinckley drew his right hand up to shield his eyes as his mother continued her testimony.

"On March 30, I received a telephone call," Mrs. Hinckley testified. "It was a reporter from The Washington Post. He said, 'Mrs. Hinckley, do you have your television on? . . . . Did you know your son John Hinckley is the man they have identified as shooting the president?' "

Hinckley's mother was the first witness in his defense lawyers' attempt to convince the jury that Hinckley was legally insane when he tried to assassinate Reagan. Other family members, including Hinckley's father, are expected to testify, along with psychiatric experts who have examined Hinckley since his arrest a year ago.

The prosecution completed the presentation of its evidence yesterday morning. Once the defense is complete, the prosecution will then present testimony from its own psychiatrists, who are expected to tell the jury that Hinckley was not suffering from a serious mental illness when he fired on Reagan.

Mrs. Hinckley testified yesterday that Hinckley twice saw a psychologist in the Denver area in the summer of 1980 but told his parents that he "felt like he didn't get any help." By that time, his mother said, Hinckley was 65 pounds overweight and complaining about a variety of illnesses--from weakness in his legs to stomachaches--for which doctors could find no cause.

In September 1980, Hinckley told his parents he wanted to enroll in a writing course at Yale University. "He had so many failures in the past we thought this would be a successful experience for him," his mother testified yesterday.

Hinckley and his parents drew up a contract, she said, in which he could sell $3,600 worth of stock in his father's oil company to pay for his schooling and expenses. In the contract, which was introduced into evidence yesterday, Hinckley said "I do pledge to try to make the coming weeks and months as productive as possible. It's now or never . . . . Thank you for the money and one more chance."

Within a week after his departure for Yale, he was back home, Mrs. Hinckley said. That same semester, the actress Jodie Foster had begun her freshman year at Yale. Hinckley's lawyers and his own prolific writings, introduced into evidence Wednesday, have described his obsession with Foster and his frustration with his unsuccessful efforts to contact her. His mother testified that her son never spoke to her about Foster.

In October 1980, Mrs. Hinckley said, everything "looked so hopeless" to her son that she was afraid he might try to take his own life. Hinckley had been consulting the psychiatrist Hopper, and the family eventually told Hopper they wanted Hinckley institutionalized, she said.

"Dr. Hopper strongly advised us not to do it. He talked us out of it . . . . Dr. Hopper said 'No, don't do it. It will really make a cripple out of John if you put him in an institution," Mrs. Hinckley told the jury.

From October through December, the prosecution contends, Hinckley stalked President Carter. Hinckley's own lawyers have said he may also have been stalking Reagan during that time.

In December 1980, Hinckley returned to his family home, "devastated . . . . this was absolutely the worst I had ever seen my son look," his mother said. Hinckley told them he had been to the funeral of John Lennon and was in "deep mourning" for his murdered "idol."

His mother recalled that after that, Hinckley spent a lot of time n his room at the family home "just sitting and staring out the window . . . or at the floor . . . or holding the cat he loves so much, petting the cat."