ebanese frustration with Israeli footdragging in the three-month-old negotiations for withdrawal of foreign troops spilled into the open today with government officials announcing an April 2 target date for reaching final agreement.

The officials made clear Lebanon had neither the power nor the intention to break off the stalemated talks. Rather, the target date apparently was designed to underline Lebanese determination to stick close to the United States, which the Beirut government has entrusted with obtaining the withdrawal of Israeli, Syrian and Palestinian guerrilla forces from the country.

Official sources, reiterating earlier support for U.S. positions worked out in concert 10 days ago in Washington, suggested that if no agreement was reached by April 2 the Lebanese government would go back to U.S. authorities for more forceful backing.

Meanwhile, the U.S. Embassy in Beirut announced that the U.S. Marines and the Israelis in Lebanon had agreed "on improved measures" to avoid confrontations. The statement said the two sides also agreed to establish "an additional channel of communication to be used for sharing operational information," The Associated Press reported.

"The mission and role of the U.S. contingent of the multinational force are not changed in any way as a consequence of this meeting," the statement said.

Lebanese officials basically see their diplomatic efforts as aimed at preventing Israel from talking the United States into watering down terms for withdrawal of Israeli troops.

Thus, the major Lebanese diplomatic effort in Washington earlier this month was designed principally to put Lebanon's views before the U.S. government, Congress and public. That is something at which Israel--but rarely previous Lebanese governments--has long excelled.

Specifically, the presence of several ministers--and veteran former prime minister Saeb Salam, representing Lebanese Moslems--was meant to frustrate Israeli Foreign Minister Yitzhak Shamir's efforts to split President Reagan and his Middle East negotiating team, headed by Philip C. Habib and his deputy, Morris Draper.

The present major stumbling block in the negotiations concerns the future of Saad Haddad, a former Lebanese Army major who heads a militia in southern Lebanon that is closely allied with Israel, which has armed, paid and supplied Haddad's forces.

Israel insists that he remain at the head of his militia. Lebanon is willing to incorporate his militiamen into two or three brigades of Lebanese troops for duty in the south, but it refuses to give Haddad a command position.

Lebanese officials, however, have made it clear that they consider the Haddad issue, although vital, as merely symptomatic of what they say are Israeli tactics that tend to reopen debate on questions that both the United States and Lebanon thought had been settled.

Prime Minister Shafiq Wazzan, according to the government press, said Lebanon's position had reached a critical "edge" or turning point and that Lebanon "had given all it could in a way that would preserve its sovereignty and integrity."