John W. Hinckley Jr., who is awaiting trial in the March 30 shooting of President Reagan and three others, attempted to hang himself yesterday in his cell at the Fort Meade stockade, a Justice Department spokesman reported.

Deputy U.S. Marshals, who keep 24-hour watch over Hinckley, "cut him down" and took him to the base hospital where he was in satisfactory condition, the spokesman said.

According to the spokesman, Hinckley never lost consciousness and suffered no serious injury in the 4:55 p.m. attempt, in which he wrapped a rolled-up jacket around a bar in an outside window of his cell.

Marshals saw what Hinckley was doing almost immediately and tried to stop him, the spokesman said, but could not get into the cell because the door lock would not work.

The marshals then reached into the cell from an exercise yard outside to cut Hinckley down, the spokesman said.

He said marshals will investigate the incident, including whether Hinckley may have disabled the door lock.

On May 27, in what also appeared to be an attempt to harm himself, Hinckley ingested an overdose of Tylenol, an aspirin subsitute, at a federal correctional facility in Butner, N.C.

Hinckley has undergone extensive psychiatric examination since his arrest at the scene of the shootings outside the Washington Hilton Hotel here.

His lawyers have acknowledged in court papers that he shot and wounded Reagan, White House press secretary James Brady, a Secret Service agent and a D.C. policeman, but have said he will contend he was insane at the time and should not be held criminally responsible.

His trial, originally scheduled for Nov. 30 in U.S. District Court here, was postponed last week until Jan. 4. Judge Barrington Parker said it would be difficult to impanel a jury during the Christmas holidays.

Hinckley was expected to remain at the hospital overnight for observation. The Justice spokesman said he did not expect the incident to affect the trial date.

No further details on the attempt or on Hinckley's activities immediately prior to it could be learned.