Philippine President Ferdinand Marcos and opposition candidate Corazon Aquino both claimed certain victory early today in an election marred by widespread reports of fraud, violence and a breakdown in counting.

After a barrage of reports on government-controlled television that virtually proclaimed Marcos the winner only hours after the polls closed at 3 p.m. yesterday (2 a.m. EST), Aquino issued a "victory statement" of her own at 1 a.m. today on the basis of an unofficial tabulation of less than 10 percent of the vote.

According to an unofficial "quick count" by the independent citizens' watchdog group, the National Citizens Movement for Free Elections known as Namfrel, as ofnoon (1 a.m. EST), Aquino was leading Marcos, 3,307,471 votes to 2,574,680, with 26 percent of the precincts reporting. Aquino's running mate, Salvador Laurel, was leading Marcos' vice presidential candidate, Arturo Tolentino, 3,032,807 to 2,507,554 votes, according to the Namfrel figures. A third vice presidential candidate Eva Estrada Kalaw was trailing with 311,120 votes. Turnout was reported to be heavy.

According to the government Commission on Elections, which as of noon had counted 13.6 percent of the precincts, the race was shaping up as follows: Aquino was leading, 561,405 to Marcos' 528,596. It said vice presidential candidate Tolentino trailed his opposition rival Laurel, 518,674 to 493,692.

After an initially rosy assessment of the election as voters trooped to the polls Friday, Sen. Richard G. Lugar (R-Ind.), the head of a 20-member official U.S. observer delegation, announced that he was "deeply disturbed" by delays in the count.

In a statement issued last week, President Reagan said that the administration would consider "significantly larger" military and economic aid to the Philippines if the election is found to be credible by the Philippine people and the government adopts basic reforms.

The official Philippine News Agency reported that 26 persons had been killed in election-related violence yesterday, bringing the death toll to 64 since the campaigning began in early December.

There were other estimates that as many as 35 persons, mostly Aquino supporters, were killed yesterday, raising the toll to 86.

"The Marcos spell is broken," Aquino declared in her victory statement. "The myth of his invincible machine has been shattered. Against his guns, against his goons and against his gold, the Filipino people have prevailed."

"The trend is clear and irreversible," Aquino said. "The people and I have won, and we know it. Nothing can take our victory from us."

The Marcos government denounced the statement as a "campaign of misinformation" being spread by Aquino. In a hastily called press conference before dawn, Deputy Information Minister Ronaldo Puno said that "whether it was designed to create instability and lead to violence or simply reflect the desperate attempts by a candidate to fool the Filipino people and thwart the democratic processes, the result is the same: confusion and distrust of our election procedures."

Puno said Aquino's "far-fetched claim" of victory with 59 percent of the vote in early unofficial returns "is an insult to the integrity of the electoral system . . . . " Puno said that Marcos was leading, 55 percent to 45 percent, but denied that the president already had proclaimed victory.

With less than 5 percent of the vote counted, Marcos had said late yesterday that partial returns "indicate that I probably have won this election."

Marcos, 68, who has ruled the Philippines for 20 years, asserted that the elections were clean and "comparatively peaceful." He invited the opposition to join him in a "reconciliation" in order to confront "two common enemies": the country's economic crisis and a growing Communist insurgency.

Marcos said that as far as he could see, American and other foreign observers sent to monitor the elections "are certainly convinced the elections have been free, honest and clean."

The conflicting victory claims arose amid the collapse of an agreement between Namfrel and the official Commission on Elections on how the quick count should be conducted. U.S. observers monitoring the election, the first genuine presidential contest in the Philippines in nearly 17 years, viewed the breakdown as "ominous" and a possible harbinger of further cheating.

The Commission on Elections, a Marcos-appointed body, is responsible for overseeing Philippine elections. Early today it demanded -- unsuccessfully -- that Namfrel stop posting results from its quick count until the dispute is resolved.

Lugar said that figures broadcast by the government television station showing Marcos ahead were "a deliberate violation of the agreement" between Namfrel and the government commission.

Lugar, the chairman of the Senate Foreign Relations Committee, said he believed that the Marcos government's strategy is to "stop the final vote" in the election. "I think the government successfully limited the vote in Manila yesterday," he said. "They're taking a look at what is going to be required to win." He added that he anticipated that the result would be "fairly close and that returns are going to filter in about as they are needed."

Lugar also said that "the control of the situation is out of the hands of the normal procedures."

"A very dangerous trend is taking place," said another U.S. observer. "The government is trying to blame all the problems on Namfrel, and the agreement on a quick count has fallen apart." He added, "The slower the count, the more suspicious it looks."

Rene Saguisag, a spokesman for Aquino, said: "This certainly must be the dirtiest election we have ever held."

[In Washington, State Department spokesman Bernard Kalb said Friday that early reports of fraud and violence were "regrettable," but he stressed that there was no way to evaluate the significance of the reports before more returns were in. President Reagan, visiting a school in Annandale, said, "It is up to the people of the Philippines to determine whether they had a fair election or not, and I am not going to comment."]

Numerous reports of election fraud and of efforts by armed men to intimidate voters flooded into Namfrel headquarters in a college gymnasium in a suburb of Manila. There, volunteers equipped with computers, telex machines and other gear were organized to conduct an "Operation Quick Count," sanctioned by the official election committee, which established its own parallel quick count operation in a government convention center.

The most widespread electoral irregularity appeared to be a slowdown in the voting process accompanied by confusion over the voter-registration lists. The result was that large numbers of voters were effectively disenfranchised, Namfrel officials said.

The national chairman of the organization, Jose Concepcion Jr., estimated that in the capital, an opposition stronghold that accounts for more than 4 million of the country's 26.1 million registered voters, about 10 percent of the voters were unable to cast their ballots. He said Namfrel volunteers assigned to poll-watching duties were prevented from entering precincts in many areas by "goons" of local pro-Marcos politicians. A number of the volunteers were beaten and at least one was fatally shot in the central Philippines province of Capiz, Concepcion said.

Namfrel said Rodrigo Ponce was gunned down while guarding ballot boxes in Roxas City in Capiz. The Namfrel quick count headquarters observed a minute of silence when his death was announced.

Violence also marred the election in Aquino's home town of Concepcion in Tarlac Province, where Namfrel declared a "failure of elections" and pulled out its volunteers. The organization said its poll-watchers were not allowed by local pro-Marcos officials to enter polling precincts in the town and that some were harassed, beaten or threatened. A U.S. election observer said local paramilitary forces fired shots into the air in one incident that ended with two American observers taking refuge in the house of Aquino's mother-in-law.

Local opposition officials in Antique Province, in the southwestern Philippines, expressed fears for the safety of two other U.S. observers, Edward Kennedy, son of Sen. Edward M. Kennedy (D-Mass.), and a cousin, William Smith. Both are members of an international observer team. The two were reported to be in a "rough area," where election violence has been reported, a U.S. official in Manila said.

In the town of Canadba in the central Luzon province of Pampanga, independent observers reported, armed soldiers speaking Ilocano, the dialect of Marcos' home province, forced voters to dip their fingers in indelible ink (used to deter multiple voting) the night before the election and told them they had already voted.

Cheating also was widespread in the capital, where observers reported vote-buying, intimidation of voters by armed men, switching of ballot boxes and seemingly systematic delays in the voting procedures.

Namfrel's poll-watching in Manila's Makati district was disrupted for much of the afternoon after several armed men stormed into a four-story elementary school being used as a polling station. They manhandled and beat several poll workers, including a Roman Catholic nun, and fired pistol shots into the air, Namfrel said. In response, Namfrel pulled many of its poll-watchers out of their stations in Makati and, in a street march, brought them to the school to stage a demonstration of support.

In many areas, Namfrel had no presence because election registrars refused to sign the necessary papers, Concepcion said. "Sometimes they put down ridiculous conditions, such as requiring the people to wear white suits and shoes," he said. "Namfrel volunteers do not go into the polling place as bridegrooms."