A citizens' poll-watching group and the government's Commission on Elections were placing opposition candidate Corazon Aquino ahead of President Ferdinand Marcos this morning as unofficial tallying from Friday's presidential elections continued.

However, government television here was stressing the results of a poll conducted by progovernment newspapers that shows Marcos winning after about 60 percent of the ballots were counted.

Election observers from the United States and other foreign countries continued to express concern over what they called slow compilation of results and incidents of fraud and violence in the voting.

Sen. Richard G. Lugar (R-Ind.), head of the official U.S. observer delegation, charged the Marcos government yesterday with trying to manipulate results from the election and said there could be repercussions for U.S.-Philippine relations. He accused Marcos officials of holding back vote results from Manila, where Aquino is strongest, in order to "shape the returns. My feeling is the count is being managed, manipulated," he told reporters.

Marcos, at a press conference yesterday, raised the possibility that he might declare the election invalid. He said he had given serious thought to voiding the election and rescheduling it.

In response to a question about what he would do if U.S. election observers found the voting to be "unclean," Marcos said: "If you're trying to move toward the point as to whether I would declare the elections invalid, and either declare that no elections had been held and continue [in office] up to 1987, or call another election, these are matters which I have thought seriously about, and as of now, I am trying to play it by ear."

Aquino, taking the offensive, called on Marcos to concede and meet with her to discuss "a smooth and quick transition of power." Marcos, however, said he expected to win, with a margin of at least 1.5 million votes.

As of 10:50 a.m. today (9:50 p.m. Saturday EST), with about 43 percent of the country's precincts reporting, the count by the citizen watch group, Namfrel, showed Aquino leading with 4,977,052 to Marcos' 4,128,520 votes. Aquino's running mate, Salvador Laurel, had 4,575,581, compared with 3,966,250 for his opponent, Arturo Tolentino.

The government-appointed Commission on Elections, in a separate count that by noon today (11 p.m. Saturday EST) had covered only 23 percent of the precincts, showed Aquino leading with 2,450,495 votes, compared with Marcos' 2,357,912. Laurel had 2,319,362 votes and Tolentino 2,226,629.

The third count by newspapers, given prominence by government television, showed Marcos leading Aquino 7,400,843 to 6,704,016. Tolentino was also said to be leading Laurel 6,527,868 to 6,409,659.

The early figures tend to be weighted in favor of the cities because those results tend to be reported before those from the outlying areas in this country of more than 7,000 islands. That means Aquino's showing could be overstated because opposition candidates traditionally have done better among city voters than rural ones. There are 26 million registered voters.

The Namfrel count included only about 10 percent of the returns from the country's administrative regions one and two which are Marcos strongholds.

Marcos accused Namfrel yesterday, of inflating the figures and committing a variety of offenses against electoral laws. He said charges would be brought.

Coupled with mounting attacks on Namfrel by other government leaders, Marcos' words were taken by some analysts here as possible preparation for rejecting any Namfrel finding of Aquino as the winner.

Aquino declared victory over Marcos at 1 a.m. yesterday, at a time when Namfrel had counted only a small portion of the vote. Later yesterday, she followed it up with a demand that he admit defeat. She said she hoped the United States would help persuade Marcos to leave.

"I shall now be sitting down and consulting widely within our nation in order to lay the foundations of the Aquino administration," she said. "I expect to have a busy first 100 days."

Aquino said figures compiled by her campaign organization, drawing on Namfrel figures and its own poll-watchers, showed that with about 6 million or one-fourth of the votes counted, she was ahead by 900,000. Marcos was leading in only two of the country's 13 administrative regions, she said.

Answering questions, Aquino said she would not accept any other group's figures if they conflicted with hers. If Marcos did not leave office, she said, she would lead daily, nonviolent demonstrations.

Sources close to the Aquino campaign suggested that her victory declaration was intended to counter suggestions by Marcos and the highly partisan government media as voting progressed Friday that he was the sure winner.

Her move appeared intended to create an additional barrier to Marcos' dismissing her challenge. It would have that effect, it is argued, by creating further expectations among her millions of supporters that she will be their next president. Although Aquino has promised demonstrations, few seem to have firm ideas on how things would unfold if Marcos remains.

Aquino's victory announcement yesterday so angered the Marcos camp that it held a predawn press conference by the deputy information minister, Ronaldo Puno, to condemn it as a threat to democracy.

Marcos met with reporters in Malacanang Palace yesterday afternoon and denounced it again. "I don't know if she's too far gone to listen to reason," he said. "You don't run for president and then say, 'These are my figures, and I stand by them,' " he said.

Marcos spent considerable time in the press conference attacking Namfrel. He said it had broken an agreement with the Commission on Elections concerning joint tabulation and was now putting out inflated figures on Aquino's electoral showing.

"Namfrel's personnel have been most active and energetic in violating the law," Marcos said. "We have the evidence."

Marcos stressed that under the constitution, formal proclamation of a presidential victor can be done only by the single-house National Assembly. Marcos' ruling New Society Movement controls the assembly. Aquino skirted questions yesterday as to whether she felt bound to follow the constitution, which was put in force under Marcos.

Marcos characterized the voting as "one of the most peaceful elections ever held in our country." He said it was virtually impossible to tamper with balloting because when the box is opened, many different people receive copies of vote-counting tallies inside.

He said there was no attempt by the government to slow down the compilation of results. His critics contend that the longer the results remain unknown, the easier it is to alter them.

"They have substantially less returns at this stage than they did in the last election," said Rep. John P. Murtha (D-Pa.), who is cochairman of the official U.S. observer team.

Referring to the returns in one town in Marcos' home province of Ilocos Norte, where Marcos was reported to have received more than 13,000 votes while Aquino received none, Murtha said: "Even in the smallest precinct, there's always one person who votes against you." He said that it was either a fabrication or a mistake.

John Hume, a member of the British Parliament from Northern Ireland who is here with an international observers group, said: "The issue here is not whether or not there have been irregularities but the extent of them and whether they have been sufficient to distort the will of the people."

"A substantial segment of the Philippines' population distrusts the electoral system as it's [now] being administered," he said. His group will make a formal statement on the election Monday.

Meanwhile, a U.S. Air Force helicopter carrying members of the U.S. observer team was reported to have been fired on while flying over the island of Mindanao, a stronghold of Moslem separatists and Communist guerrillas. In the helicopter were Sen. John F. Kerry (D-Mass.) and retired Adm. Robert Long.

[In Washington, State Department officials said a nonvital helicopter part near the windshield fell off and made a noise, The Associated Press reported. No one was reported hurt in the incident.]