A U.S. District Court judge yesterday scheduled trial to begin on March 9 for John W. Hinckley Jr., accused of attempting to assassinate President Reagan, but a federal appeals court promptly canceled the date.

The appellate court said the March 9 date might not give prosecutors enough time to appeal an earlier decision that blocked them from introducing some evidence they want to use in Hinckley's trial.

Hinckley has admitted that he fired the shots from a .22-caliber pistol that struck Reagan, White House Press Secretary James Brady, a District police officer and a U.S. Secret Service agent outside the Washington Hilton Hotel last March 30. He claims he was insane at the time and thus should not be held criminally responsible for his acts.

His trial has been delayed for months while prosecution and defense lawyers skirmished over whether certain pieces of evidence might be offered in the case.

Judge Barrington D. Parker, ruling on two key questions, decided last November that FBI agents had illegally questioned Hinckley after his arrest last March 30. Parker also found that prison officials at Butner, N.C., had illegally seized documents from Hinckley.

On Tuesday, a three-judge appellate panel agreed with Parker that the government cannot use either Hinckley's statements to the FBI or the seized documents as evidence at the trial.

In an unusual move, the panel the same day sent the case back to Parker, before prosecutors had made any decision about seeking further review by the full 11-member appeals court.

According to court rules, the government has 45 days to seek review.

The government had asked the appellate court Wednesday to recall the case so that prosecutors would have more time to consider appeals, but the appellate court had not acted on that request by the time Parker began a hearing on the case yesterday.

Saying "I think it's time to proceed and proceed immediately," Parker set the March 9 trial date. He told lawyers he intended to begin then unless he heard otherwise from the appeals court.

"I get a message from the Court of Appeals and the message is there's a green light," Parker said, apparently relying on the appellate court's unusually quick action in returning the case to him.

Five hours later, the appeals court issued a brief order, saying "the early trial date may operate to deprive the government of its opportunity to seek further review of the issues on these appeals . . . "

The panel then recalled the case from Judge Parker, which lawyers said removes the case from his jurisdiction and thus cancels the trial date as well as other dates he had set for pretrial court filings by prosecution and defense lawyers.

Chief Judge Spottswood W. Robinson III and Judges J. Skelly Wright and Patricia Wald decided the case in the appeals court and issued yesterday's order.

Hinckley, who is being held at the army stockade at Fort Meade, Md., was present in court yesterday, wearing a now familiar white bulletproof vest under his navy blue sport coat.

He nodded his head in agreement as Parker noted that in the 11 months since the shooting Hinckley has been "examined and reexamined" by a battery of experts on mental illness in preparation for his trial.

U.S. Attorney Stanley S. Harris said late yesterday that his office must get approval from the Department of Justice before it can ask the full appeals court to review the issues upheld by the panel Tuesday.