WASHINGTON (AP) _ Presidential assailant John W. Hinckley Jr., giving his first public testimony, won court permission Thursday to start negotiations to hire assassination buff Mark Lane as his lawyer.

''It is my belief that I have the right to choose who will be my attorney,'' Hinckley told U.S. District Judge June L. Green at a hearing on his request to dismiss his longstanding defense team and begin discussions with Lane.

Green gave Hinckley permission to interview Lane and any other prospective attorneys despite reservations expressed by officials of a mental hospital where he has been held since he was acquitted in 1982 by reason of insanity of shooting President Reagan and three others in 1981.

A psychiatrist at St. Elizabeths Hospital testified that Hinckley still suffers from a serious mental illness and has been moved from a dormitory- style room to a maximum-security ward because he couldn't handle privileges he had previously enjoyed.

Hinckley didn't identify Lane until the end of his testimony when a hospital lawyer asked: ''Are you aware that in fact he has written a number of books about political assassinations?''

''I know of one book he has written,'' Hinckley told hospital attorney Janet L. Maher.

''What book is that?'' the judge interjected.

''Do you want me to just give this person's name because we are going to lead into that?''

When the judge indicated she wanted an answer, Hinckley said: ''He has written a book called 'Rush to Judgment.' His name is Mark Lane.''

Lane's 1968 book, ''Rush to Judgment: A Citizen's Dissent,'' questioned the findings of the Warren Commission that Lee Harvey Oswald acted alone when he killed President Kennedy in 1963.

He has also written numerous articles, including a 1980 book about the 1978 Jonestown massacre in Guyana.

Maher, who argued that letting Hinckley interview prospective lawyers ''presents a unique opportunity for exploitation,'' reminded Hinckley that Lane had written a number of books about people he had represented in criminal cases.

''I don't think it's a crime that he's written these books and interviewed these people,'' Hinckley said. ''I am sure that the subjects he has written about at some point gave their consent.''

''I am capable of deciding whether I want my story told and it is not the hospital's say to dictate whether I can do that,'' said Hinckley, who spoke lucidly and appeared relaxed on the witness stand.

''I should at least be permitted to talk to the man,'' Hinckley said. ''If we don't get along, it stops right there.''

Hinckley said that he wanted to hire Lane because ''he has represented some people who are famous to the general public.'' These clients gained their noteerity ''as criminals, in the criminal world,'' he added.

Among Lane's clients was James Earl Ray, who shot the Rev. Martin Luther King Jr. in 1968 - a fact Hinckley acknowledged knowing. Lane represented Ray on an attempt to get a retrial of the case.

Earlier in his testimony, Hinckley said he had no money to hire an attorney because he had depleted all the money in a fund set up for him by his family to pay Vincent J. Fuller to defend him during his 1982 trial.

''I am indigent now, but that doesn't mean that in the future that I won't be able to make any money,'' Hinckley said.

Dr. Raymond F. Patterson, testified that Hinckley was competent to pick his own attorney.

But Patterson expressed concern that people seeking to exploit a connection with Hinckley would interfere with the treatment he is receiving at St. Elizabeths.

A psychiatrist who until recently has treated Hinckley since 1982, Patterson testified that he ''continues to have difficulty in his judgment'' and has ''difficulty learning from his past experience.''

He can't ''differentiate famous from infamous,'' Patterson said. ''He does not have a clear perception of how he is seen by others.''

''He has had to resume a higher level of restriction,'' Patterson said. At one point, Hinckley was living in a dormitory-style room and in late 1986 hospital authorities allowed him to spend time during the Christmas holidays with his family at a townhouse in suburban Virginia.

A request for a similar weekend visit over the Easter holiday the next year was met with strong opposition by the Secret Service, which wasn't formally told of the Christmas visit.

The hospital dropped its request after prosecutors produced evidence that Hinckley had corresponded with serial killer Ted Bundy, who was executed earlier this year in Florida.

The hospital also abandoned plans to take Hinckley on an outing with other patients last summer after another cache of writings was found in his room.

Patterson said Hinckley was placed in a maximum-security ward because he had ''difficulty handling the privileges'' previously given to him.

Hinckley was acquitted in 1982 by reason of insanity of shooting Reagan, then-presidential press secretary James Brady, a Washington police officer and a Secret Service agent. The shooting has left Brady partially paralyzed.

After the hearing, Fuller, saying he thought Hinckley did well as a witness, said he was glad to be off the case. ''I am relieved.''

''He wanted new counsel, he's entitled to it. I did not want to stand in his way.''