The Philippine Embassy, once known in diplomatic circles for its absentee ambassador, is expected to assume a much more active role when its new envoy arrives, according to diplomats and State Department officials.

The new ambassador, Emmanuel Pelaez, 70, a former vice president and foreign minister in the 1960s, replaces the brother-in-law of deposed president Ferdinand Marcos, Benjamin Romualdez. Pelaez is expected to arrive within the week.

Asked in a recent telephone interview in Manila about specific changes, he noted the frequent absences of the former ambassador and said, laughing, "I hope to be a resident ambassador."

Said one administration official: "We expect it [the embassy] to be much more high profile. Romualdez was never here. When he was, he had a different agenda: trouble-shoot for Marcos."

Romualdez's absence left the embassy functioning at a minimal level. "Their ability to understand developments in Washington, the roles of the different branches of government, their ability to influence and react to developments in a constructive way were all limited," said one administration official.

The embassy staff was often frustrated because all decisions had to be cleared by Romualdez, who was usually in Manila.

The word is out, however, that Pelaez is going to change all that. He is expected to find replacements for many of the senior embassy officials. He has said he would improve press relations, which were strictly regulated under Marcos. The Aquino government has singled out "the government propaganda machine" set up under Marcos as one of the targets of change.

The new deputy chief of mission, Raul Rabe, 46, has already arrived from Hawaii, where he was the consul general in Honolulu. Rabe, a career foreign service officer who has previously served in Washington, was the first Philippine diplomat abroad to distance himself from Marcos on the first day of the military rebellion, Feb. 22, joining the calls for Marcos' resignation.

Pelaez, a lawyer and former minister of state in the Marcos government, was one of the first former Marcos associates to endorse Aquino last year for the Feb. 7 presidential election. Four years ago, he survived an assassination attempt that he believes was carried out by hired gunmen of Marcos' close associates because of his opposition to a monopoly of the country's coconut industry.

Pelaez is perceived as a senior statesman who combines a strong nationalist sentiment with long and respected government service, according to diplomats and U.S. officials. During the first sessions with Washington to renegotiate the 1947 agreement with Manila on two key U.S. military bases, Pelaez led the Philippine panel and earned a reputation as a tough negotiator, U.S. officials said.

"He's not a leftist flake nor is he a member of the traditional right," said one official. He added that Washington "made a special effort" to speed up the acceptance of Pelaez's credentials.

On one of the most important bilateral issues, the strategically located U.S. military bases, Pelaez appears to be in agreement with Aquino to honor the agreement until it expires in 1991.

Pelaez laid out his position in a paper published in January by the Philippine Council for Foreign Relations, a private nonpartisan organization set up last summer to study and discuss "problems of international relations for the avowed purpose of advancing the national interest."

Pelaez is in favor of letting the agreement run its full course. Then the Philippines has to decide "whether to terminate the American military presence in the Philippines or to allow for a specific number of years under conditions consistent with her sovereignty and national dignity."

If the United States wishes to maintain a military presence, Pelaez recommends that the two sides negotiate a new agreement concerning the bases that the Filipino people would consider in a national referendum.