BEIRUT, AUG. 2 -- Gunmen shot and killed Christian President Amin Gemayel's Islamic affairs adviser in Moslem west Beirut today and a bomb shattered windows of the empty Saudi Embassy, police said.

In eastern Lebanon, thousands of Shiite Moslem extremists rallied to protest the deaths of Iranian pilgrims in Mecca.

Mohammed Shukair, a Sunni Moslem who has advised Gemayel on Islamic affairs since the president took office in 1982, was shot dead by assailants who broke into his house, police said.

They said Shukair was rushed to the American University Hospital, where he was pronounced dead. No other details were available.

Shukair, in his mid-50s, was a moderate who advocated dialogue as means to end Lebanon's 12-year-old civil war, which has claimed more than 125,000 lives. His slaying was expected to dim chances of reconciliation between Moslems and Christians.

The bomb that damaged the Saudi Embassy was tossed into the garden of its walled compound in west Beirut's Manara residential district. No casualties were reported. will not escape this massacre without punishment," said the typewritten Arabic statement delivered to a Western news agency.

"We consider the United States responsible for this massacre and it will bear the consequences of its directives to its surrogates," it said.

AP-BA-08-02 1908EDT