The Polish wife of a Palestinian being held by British police in connection with the attempted bombing of an Israeli airliner last month has told friends that he made frequent visits to Lebanon, Libya and Syria, ostensibly as a journalist.

Postcards that Nezar Hindawi sent his wife, Barbara Litwiniec, since she returned to Poland in 1984 establish that he traveled regularly to those three Arab countries and that he was in Syria as recently as late February, according to the woman's friends, who asked to remain anonymous. Litwiniec, 30, married Hindawi in December 1980 in London.

West Berlin police disclosed May 6 that Hindawi's brother, Ahmed Nawaf Mansour Hasi, had confessed taking part in a bombing in Berlin March 29 that injured seven persons. The police depicted Hindawi as the ringleader of the attack and reported him as telling police that the Syrian Embassy in East Berlin supplied the explosives for the attack.

British authorities, acting partly on the basis of information supplied by Israel, have said that they suspect both Libyan and Syrian involvement in the April 17 attempt to smuggle a bomb onto an El Al jetliner at London's Heathrow airport. But the British have refused to elaborate on the evidence, which is alleged to link Hindawi to the two radical Arab states.

Hindawi, 31, a Jordanian-born Palestinian, was arrested in a London hotel on April 18, the day after security officers at Heathrow airport seized Hindawi's pregnant Irish girlfriend, Anne-Marie Murphy, as she attempted to board El Al's Flight 016 to Tel Aviv. Her hand luggage was found to contain a bomb made of thinly rolled plastic explosive and a sophisticated microchip timer that authorities said was sufficient to destroy the Boeing 747 and its 340 passengers.