Georgia Sen. Sam Nunn, ranking Democrat on the Senate Armed Services Committee, declared yesterday that "the Philippine people want President Marcos out and they have elected Corazon Aquino," and he asked President Reagan in a letter to declare that U.S. aid will end if the will of that nation's voters is thwarted through fraud.

Nunn's letter, with new statements by Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.), added to growing pressure on Reagan to modify the "hands-off" posture that the White House has taken this week toward fraud in the Philippine balloting.

Comments by officials with the presidential party in California, where Reagan is on vacation, suggested the White House stance may have begun to shift. Sources there and in Washington said special White House emissary Philip C. Habib will convey to Marcos in private conversation U.S. "displeasure and disappointment" with the way the elections were conducted.

Nunn, in a letter to Reagan containing strong language for a political moderate, said that "Marcos or forces allied with him are in the process of making an all-out effort to steal the election by massive fraud, intimidation and murder."

An aide said Nunn, who has followed Philippine affairs for many months as a member of the Armed Services and Intelligence committees, wrote his letter after being briefed Wednesday by the Central Intelligence Agency and speaking to many knowledgable persons in and out of government.

Should Marcos succeed in "taking away the election by fraud," Nunn said, "it will be a disaster for American interests in the Pacific. The church has turned against him, the business community has turned against him and the people have turned against him -- he has lost his legitimacy as a leader."

Nunn added that the "extremely important" naval and air bases in the Philippines "can serve us effectively only if the Philippine people want us there."

Senate Majority Leader Robert J. Dole (R-Kan.), speaking in Los Angeles, said that because of "the unsettled situation" in the Philippines, the administration should accelerate "contingency planning" to relocate U.S. military units stationed at the Philippine bases to facilities elsewhere in the Pacific.

Dole said he will introduce legislation calling for such a study when Congress reconvenes next week.

Lugar, who was cochairman of the U.S. election monitoring team at last week's Philippine elections, said in Muncie, Ind., that Reagan "apparently was not well informed about there being fraud on both sides," referring to a comment during the presidential news conference Tuesday night. In his analysis, Lugar said, "the predominance of fraud" was on the side of the Marcos government.

Addressing what is reported to be a central concern of the White House -- that lack of support for Marcos would create a chaotic and detrimental situation like that in Iran after the fall of the Shah -- Lugar told a group of Indiana high school students that "The Philippines is not like Iran. In the Philippines, we have a genuine democratic alternative. For the first time in 17 years [evidently since Marcos' second election as president in 1969] there is a genuine democratic option in the Philippines."

White House officials in California said Habib, who left Washington for Manila at 5 p.m. yesterday in a U.S. Air Force plane, will refrain from public condemnation of the election process because Reagan thinks that this could trigger riots and possible revolution in the Philippines.

"But Marcos also needs to know that the president is not happy with the way the elections apparently were conducted," said a senior official. "He needs to know he has does not have a blank check from us."

The Reagan administration remains "neutral" on the outcome of the election, officials in California said. But some conceded that the president had confused the message of neutrality at his news conference by saying that fraud "could have been . . . occurring on both sides."

The latter statement has been denounced by Aquino and trumpeted by Marcos forces as an endorsement.

White House spokesman Larry Speakes today resisted efforts by reporters to elicit a clarification of this statement and reiterated U.S. neutrality in the election. But a senior official said that it would be a "mistake" for Marcos to reach the conclusion that Reagan approved of the election process.

"Except for that 'fraud on both sides' business, which just kind of slipped out, the president's message Tuesday was not an endorsement of Marcos," the official said.

"The problem is that Marcos has been a friend in the past, even though he's now damaged goods, and the president is always reluctant to abandon a friend," the official said.

Officials said that Habib had stressed the importance of U.S. neutrality in his brief discussion with Reagan at the White House on Wednesday morning. Habib reportedly said to the president that it was "important not to get out ahead of the Filipino people."

White House officials expect that the president will be called upon to make further statements after Habib returns from the Philippines, probably at the end of next week. Staff writer Don Oberdorfer reported this story from Washington, Lou Cannon from California.