Because an important witness failed to appear, a court Thursday adjourned until next week the trial of a Lebanese man charged with the 1985 TWA hijacking and murder of a U.S. Navy diver.

Less than an hour after the trial of Mohammed Ali Hamadi resumed today, chief judge Heiner Mueckenberger recessed the proceedings until Wednesday.

The trial, under heavy security in a specially constructed prison courtroom, began Tuesday.

Both of the trial's first two sessions have been cut short, raising prospects the proceedings could extend into next year. Already, officials have scheduled court days into December and say more could be added.

Hamadi, a Lebanese Shiite Moslem, is on trial for murder and air piracy in the June 1985 TWA hijacking. During the ordeal, 39 Americans were held hostage 17 days and U.S. Navy diver Robert Stethem of Waldorf, Md., was murdered after gunmen forced the Athens to Rome flight to land in Beirut.