Students and professors at the American University of Beirut went on strike today, demanding intense efforts to find two British teachers missing since Friday. A British Embassy spokesman said there were no leads in the case.

Leigh Douglas, 31, a professor of political science at the university, and Philip Padfield, 40, the director of a language center, were last seen walking home from a popular West Beirut pub frequented by students and journalists. The men are presumed to have been kidnaped.

The century-old university has received extensive American financial support. Its American faculty members frequently have been targets of Beirut's extremists.

This time, said a colleague of Douglas, the 450 faculty members voted to strike until "we are satisfied" that police and militia are making a rigorous search. The affiliated medical school and hospital are to shut if no results are reported by Monday.

No group has claimed responsibility for siezing the men and no demands have been made, the British Embassy spokesman said. Ambassador John Gray met with senior leaders in the Moslem-controlled half of Beirut today to seek assistance in the search.

A French announcement yesterday of withdrawal of its cease-fire observers here underlined a continuing exodus of foreigners from Lebanon. The British Embassy reemphasized a standing advisory to its nationals not to travel or reside in west Beirut, south Lebanon or the Bekaa Valley unless they "have compelling reasons to do so."

Two explosive charges dismantled near the offices of British Airways and the British Council over the weekend have raised concern over the safety of 50 Britons still living here.