BEIRUT, JUNE 5 -- -- Parliament Speaker Hussein Husseini resigned today over dissatisfaction with President Amin Gemayel's response to the assassination of prime minister Rashid Karami.

The surprise resignation of Husseini, 50, the top Shiite Moslem in the government, underlined Moslem demands for a full investigation of the bomb blast that killed Karami aboard an Army helicopter Monday and Syrian pressure aimed at isolating Gemayel, a Maronite Christian.

Shiite sources close to Husseini said he was angered by Gemayel's failure to move the Army against the Christian militias, suspected of being behind the assassination. Moslem officials are unanimous in their suspicion that the assassination was the work of agents, or sympathizers, of the Christian militias. No evidence, however, has surfaced implicating them.

Political sources said Syrian Vice President Abdul Halim Khaddam had prompted Husseini's resignation during a meeting with the speaker and Moslem ministers after Karami's burial Wednesday. Khaddam reportedly scolded them for rushing to appoint an acting prime minister, in consultation with Gemayel, to avert a constitutional void. After conferring with Sunni Moslem political and clerical leaders, Husseini asked Gemayel to name Education Minister Selim Hoss, a Sunni Moslem, as acting prime minister.

Sources close to Husseini said he had asked Gemayel to at least deploy the Lebanese Army along the coastal road north of Beirut to Tripoli so that Moslem officials could travel overland to Karami's funeral without having to pass through Christian militia checkpoints. The president's response was that he could not secure the highway, and the Army's lifting of a state of general alert yesterday was seen as another indicator that Gemayel would not assert his authority over the militias, the sources added.