TODAY, ONLY two days after American television viewers watched police and Secret Service agents subdue a suspect alleged to have shot the president and three others, the trial of Bernard C. Welch -- accused murderer of Dr. Michael Halberstam -- opens in D.C. Superior Court. What connects Monday's tragedy and Wednesday's trial has nothing to do with the facts of either episode or with the suspects involved. Both men enjoy the same rights as any American at such times: an absolute presumption of innocence until found guilty after a fair trial, at which every legitimate measure of assistance to the defense has been made available.

The link between the Welch trial and the Hilton Hotel shootings lies in the dilemma of minimizing potentially prejudicial pretrial publicity. The defendant, Mr. Welch, complained in a tape-recorded interview with a reporter from this newspaper last week that the press had "already found me guilty. I just don't believe I'll ever get a fair trial in the Washington area. It's going to be a farce . . . . "

The allegation could not be more serious, and Mr. Welch's attorney, Sol Z. Rosen, has filed a pretrial motion to shift jurisdiction from Washington on grounds that adverse publicity has already made it impossible to empanel an unbiased jury. The prosecutors disagree, and Chief Judge H. Carl Moultrie, who is presiding at the Welch trial, will have to rule on the request. Related to the motion are other defense requests of more immediate and disturbing concern. Mr. Rosen has asked that all pretrial hearings be closed to the press and has subpoenaed the reporters -- and all stories on the case from both The Post and The Star. A secret trial remains a dubious trial, in our opinion. There is no reason for one in the Welch case, especially since the defendant himself has raised the ante in playing pretrial publicity poker on more than one occasion.

First came his voluntary interview with Life magazine, for which Mr. Welch received about $8,000 in return for assigning the magazine the right to exclusive use of certain personal photographs. Since then, he has given other interviews, including the one to this newspaper, and has arranged the sale of rights to a book on his life to a New York writer.

Under the circumstances, what would be the logic of closing pretrial or trial proceedings in his case to the working press? Is it that, unlike others, they have not paid for the privilege of reporting him?

As for Mr. Welch's request for a change of venue and other pretrial motions, Judge Moultrie needs no assistance from us in determining their merits. Whatever its outcome, though, the Welch case has reminded the press again of how carefully it must proceed during such sensitive proceedings if judges, lawyers on both sides and the public are not to put the media on trial instead of the defendant. Since the Welch case will probably not be the last dramatic trial to be held in Washington this year, today is a sadly appropriate day to remind ourselves that all parties involved -- prosecution, defense, judge, jury, and the press -- bear responsibility for proving that pretrial publicity, however generated, need not prevent a fair judgment in open court.