The Philippine legislature last night officially took over responsibility for canvassing vote counts and declaring a winner in the presidential contest between President Ferdinand Marcos and opposition candidate Corazon Aquino.

The Batasang Pambansa, or National Assembly, declared itself a National Board of Canvassers, in accordance with the constitution, to tally the returns from Friday's election and proclaim a winner within 15 days of the start of canvassing.

Opposition and government sources said the system heavily favors Marcos, since his ruling New Society Movement controls two-thirds of the assembly, and challenges are to be settled by majority vote.

Thus, the sources said, false returns could be accepted as genuine by the assembly and used to proclaim Marcos' reelection.

"The people will watch the Batasang," Aquino warned in a speech yesterday. She said the legislators "must now act as the representatives of the people they claim to be. There will be no room for a dictator's puppet in the new Republic of the Philippines."

The move by the National Assembly capped a day of mounting tension in which two persons were killed, one in the capital and the other in Antique province.

An unknown gunman, apparently firing twice from a building, killed an Aquino supporter, Arsenio Toribio, and grazed the forehead of another, Lilibeth Quijano, hospital authorities said.

The two were riding with about 50 other persons on a flatbed truck used as a stage for Aquino during the outdoor mass and prayer rally an hour before, witnesses said. They said Toribio was shot in the chest through a sign he was holding that read, "Marcos Concede." Aquino by then was far from the site of the shooting.

[In the second shooting death of an opposition supporter, Evelio Javier was gunned down by six masked gunmen in the town plaza of San Jose in Antique province, his brother told the Aquino campaign headquarters in the capital, United Press International reported] .

"We are going to take power," Aquino said in a speech at the rally, attended by about 5,000 people in the business district of Makati. "The people have won this election. The only question left is when I should take power in their name."

She said that if Marcos cheats her of victory, "we must all fear the consequences."

A poll tally by an independent civic group, The National Citizens' Movement for Free Elections, known as Namfrel, put Aquino ahead early today with 6.65 million votes to Marcos' 5.97 million, or about 53 to 47 percent with 66 percent of precincts reporting.

In a separate tally for the vice presidential race, Aquino's running mate, Salvador Laurel, was leading with 6.43 million votes to 5.62 million for Marcos' running mate, Arturo Tolentino.

However, this tally includes the vote from mostly urban areas, including the metropolitan Manila region where Aquino was expected to do well, and fewer returns from more remote and rural areas that are likely to be pro-Marcos.

A count by the Commission on Elections, or Comelec, the Marcos-appointed body in charge of administering and arbitrating elections, had Marcos narrowly leading Aquino, by 3.81 million votes to 3.61 million, or about 51 to 49 percent with 35 percent of precincts reporting. It also had Tolentino leading Laurel by 3.59 million votes to 3.46 million.

The Comelec count has been troubled by slow returns and an employes' walkout over alleged falsification of results.

The two rival unofficial counts were intended to establish a winner quickly in the public mind and allay fears of manipulation if returns were delayed, "but they have been slowed because of widespread irregularities. Two other unofficial tallies by pro-Marcos groups have the 68-year-old president well ahead.

Marcos yesterday ruled that all four unofficial counts could go ahead while the official tabulation by the National Assembly proceeded.

At least 2,000 Aquino supporters gathered outside the assembly building last night for a vigil while the legislators conduct the count. They chanted Aquino's nickname, Cory, and booed pro-Marcos legislators. Riot police equipped with helmets, shields and batons, a truck-load of Army troops in combat gear and hundreds of plainclothesmen with revolvers bulging at their waistbands stood ready to intervene.

The assembly formed a Board of Tellers, consisting of four opposition legislators and four from Marcos' ruling party. The board is charged with examining election returns, called "certificates of canvass," and filing any challenges to their authenticity.

Proclamation is to take place within 15 days of the start of the canvassing. The assembly formally opened the process yesterday with 60 of the country's 137 certificates of canvass in the legislature's possession and the rest still to be delivered by cities and provinces.

The assembly voted to adjourn the session until this afternoon without beginning to count the returns, so as to allowl such observers as Namfrel officials to attend.

Some Aquino supporters expressed apprehension that, through massive vote-buying, electoral fraud and intimidation of voters, Marcos would hold on to the office he has occupied for 22 years.

"Mr. Marcos has stolen this election," Ernesto Maceda, a former senator and a supporter of Aquino for president, charged. "Cory Aquino is the legitimate president of this country," he told reporters. "We call on all Filipinos not to recognize the legitimacy of Mr. Marcos."

An opposition legislator expressed concerned that "the Batasang will just be lending itself to a fraudulent election."

For many Filipinos, including some members of Marcos' party, the damage already may have been done.

"It's a pyrrhic victory for Marcos," one insider said. "He's lost so much." He said Marcos' image has been "shattered" by what he said was massive cheating -- under the full glare of foreign observers and journalists -- that has been necessary thus far to avert a sweeping Aquino victory.

Observers said further fraud was still possible through the switching of election returns, a prospect that has prompted thousands of Aquino supporters to hold 24-hour vigils at canvassing centers.