John W. Hinckley Jr., in what he described as "my own decision," told a federal judge yesterday he will not seek immediate release from St. Elizabeths Hospital, where he has been confined since a jury found in June he was legally insane when he shot President Reagan.

In a single-page statement filed in U.S. District Court, Hinckley voluntarily waived his legal right to a hearing, scheduled for Monday, at which he could have tried to persuade Judge Barrington D. Parker that he was entitled to release.

"After consulting with my attorneys, I made my own decision about whether to exercise my right to such a hearing," Hinckley said in the court filing, which was signed by him and by his defense lawyers, Vincent J. Fuller and Gregory B. Craig.

Hinckley's decision appears to clear the way for Parker to enter a formal order committing him indefinitely to St. Elizabeths on the grounds that he is mentally ill and dangerous. Hinckley would then have the right to come to court every six months to try to prove to Parker he is ready to be released.

However, various sources said yesterday that there was some confusion about what the next step in the case will be. For example, sources said, it may be necessary for Hinckley to appear in court Monday to formally waive his right to a release hearing, even though he has done so in court papers. That waiver must ultimately be accepted by Parker.

In a report submitted to the judge on Monday, doctors who have been evaluating Hinckley at St. Elizabeths said Hinckley has a severe and chronic mental disorder and remains a danger to himself as well as to others, in particular actress Jodie Foster.

According to sources, the doctors determined that symptoms of his illness include a "pattern of fixed grandiose, homicidal and suicidal ideas" he holds about Foster. The morning of Hinckley's attack on Reagan, he left in his hotel room an unmailed letter to Foster in which he told her he hoped to win her respect and love by "this historic deed."

Hinckley's defense lawyers yesterday filed additional papers under seal with the court in which they said, according to informed sources, that they would not contest the hospital's findings. Both Hinckley's lawyers and his parents have said they would not seek Hinckley's release until doctors determine he is well and no longer dangerous.

The defense has proposed that the prosecution join with them in a formal agreement to accept the accuracy of the hospital's findings. The prosecution is expected to file papers with the court today in response to the defense proposal.

Hinckley has been in custody in a maximum security ward at the John Howard Pavilion at St. Elizabeths since June 22, one day after a jury found he was legally insane when he shot Reagan, his press secretary James Brady, U.S. Secret Service Agent Timothy McCarthy and former D.C. police officer Thomas K. Delahanty on March 30, 1981.

Parker was required by law to commit Hinckley to the hospital for 50 days, during which time doctors there were ordered to determine whether he remained mentally ill and dangerous to himself or others and to submit their findings to the court. At the hearing scheduled for Monday, Parker would then decide whether Hinckley was entitled to release.

During Hinckley's trial, the prosecution was required to prove, beyond a reasonable doubt, that Hinckley was sane when he attacked Reagan. To seek his release at Monday's hearing it is generally agreed that Hinckley would be required to show independently and by a preponderance of the evidence that he is now sane.

There is a continuing debate about the state of the law on those burden of proof issues--particularly as they applied in Hinckley's case. It appeared yesterday that the government, anxious to avoid any future legal challenges to Hinckley's continued confinement, wanted to deal with those differences before entering into any agreement with the defense lawyers.