Lawyers for John W. Hinckley Jr. and federal prosecutors argued yesterday over whether the presidential assailant's ongoing relationship with a former mental patient could make him dangerous if he wins extended and unsupervised visits to his parents' home in Williamsburg.

The debate came as a federal judge yesterday began hearing testimony on Hinckley's request to spend more time away from St. Elizabeths Hospital, the Southeast Washington psychiatric facility where he has lived since a jury found him not guilty by reason of insanity in the 1981 shootings of President Ronald Reagan and three others.

Hinckley, 49, sat attentively in U.S. District Court as lawyers and doctors analyzed his mental state and personal relationships. He showed no emotion.

Prosecutors contended that Hinckley may have been deceptive about his ongoing interest in Leslie deVeau, who was confined at St. Elizabeths after she was found not guilty by reason of insanity in the 1982 killing of her 10-year-old daughter. She and Hinckley met when both were patients, and had a romantic relationship. DeVeau was released in 1990 and broke off the romance several years later, according to hospital officials.

According to prosecutors, the public should worry about Hinckley's continued desire for a romantic relationship with deVeau because he long ago admitted that he shot Reagan as part of his obsessive interest in actress Jodie Foster.

But a psychiatrist, who interviewed deVeau and Hinckley last week, testified that both want to maintain their long-standing friendship, even though Hinckley said he regrets their breakup.

Robert Keisling, a former St. Elizabeths medical director hired by the Hinckley family, said deVeau explained to him that she broke off the romance because she could no longer handle the Secret Service scrutinizing her financial records, her trash and her travels. The Secret Service has continued to monitor Hinckley's conduct on and off the hospital grounds.

Keisling quoted deVeau as saying that she cringed reading about her past in newspaper articles about Hinckley.

"She concluded she was never going to have the privacy she needed as long as she was the girlfriend of John Hinckley," Keisling said. "I don't think he's entirely happy with her decision . . . but he understands it. They both continue to get a lot of support from each other . . . but there's no sex, no romance."

DeVeau did not attend the court proceedings, which are expected to continue today and tomorrow. Attempts to reach her for comment were unsuccessful.

Hinckley has asked the court for permission to stay with his parents and siblings in their Williamsburg home without hospital staff supervision for four days at a stretch every two weeks. His attorney contends that the visits are the next appropriate step in treatment for a man whose illness has been in remission for years.

U.S. District Judge Paul L. Friedman will decide the matter. Last year, Friedman agreed to permit Hinckley to begin a series of similar, unescorted visits with his parents in the Washington area. But the judge ordered that Hinckley have no contact with deVeau while on those trips.

The government could face an uphill battle in trying to block an expansion of Hinckley's liberties. The hospital supports a version of Hinckley's newest request, though it would start with two "test" trips of four days' duration. Officials would consider additional visits after reviewing Hinckley's behavior on those stays.

The government's experts acknowledge that Hinckley has been in good mental health for more than a decade, his attorneys note.

Attorney Barry Wm. Levine said there is "absolutely no evidence" of Hinckley being a danger to himself or others. Hinckley has proved his stability because he has completed eight successful local visits to see his parents without staff supervision in the past year, Levine said.

"It's undisputable that on all of the visits, Mr. Hinckley punctiliously complied with all the rules and conditions set by the court . . . and all progressed without incident," Levine said. "Mr. Hinckley has proven this court right."

Prosecutor Thomas Zeno focused yesterday on Hinckley's recent statements to other psychiatrists and therapists that he was still in love with deVeau. Zeno quoted Hinckley as saying he recently chose not to ask deVeau whether she would come to visit his parents' home in Williamsburg if he was there, "because maybe I don't want to know the answer."

Keisling said there is no parallel between Hinckley's delusional obsession with Foster more than two decades ago and his 17-year friendship with deVeau.

"That was fantasized," the psychiatrist testified. "This is very real. They share a lot of the same experiences."

Keisling said that, if the court allows it, deVeau may want to visit the Hinckley family when their son is visiting.

"It would be a visit of an old friend," Keisling said. "They might have dinner. She might spend the night. But she would not sleep in the bed with Mr. Hinckley. There would be no sex and no romance."

John and Jo Ann Hinckley, parents of John Hinckley Jr., who shot President Ronald Reagan in 1981, leave the courthouse.