Opposition presidential candidate Corazon Aquino launched her campaign against President Ferdinand Marcos today with a pledge to seek justice for her late husband amid signs of continuing tension between Aquino and her running mate, Salvador Laurel.

"I'm not out to seek revenge, but I want justice for Ninoy and justice for all the victims of Marcos," Aquino said in this provincial capital 66 miles south of Manila. Ninoy was the nickname of her husband, opposition leader Benigno Aquino Jr., who was shot at the Manila International Airport Aug. 21, 1983, while in the custody of military guards.

A court this month acquitted the armed forces chief of staff, Gen. Fabian Ver, 24 other military men and one civilian of involvement in the slaying and a later cover-up.

In a press conference before setting out on her first campaign swing, Aquino said she still considered Marcos "my number one suspect in the assassination of Ninoy."

Aquino opened the campaign with Laurel a day after they announced that they had patched up a rift and agreed to form a unified ticket. In a compromise to achieve unity, Laurel withdrew his candidacy for president and Aquino agreed to join Laurel's political party, the United Nationalist Democratic Organization. However, it was clear today that tension remained between the two, and the campaign appeared to get off to a slow start with the visit to Laurel's home province of Batangas.

Before the visit, the two candidates appeared together at a news conference to explain their decision to reunite after a split had raised the prospect of two opposition challengers to Marcos in an early election set for Feb. 7. Laurel continued to blame the split on Aquino's refusal to join his party, known as Unido, after he had agreed to give up his presidential ambitions. He said unity was achieved when she "reconsidered her decision" and agreed to run as the Unido candidate for president.

Aquino said that after consulting friends and receiving numerous messages expressing disappointment with the opposition, she concluded that Filipinos deserved "the best possible opportunity to end the Marcos dictatorship." She said that she agreed only to join Unido and that other issues between the two camps were "to be talked about when we achieve victory."

Laurel aides expressed concern that unless both Aquino and Laurel ran on the ticket of the established Unido party, the team might forfeit legal status that provides for party inspectors at polling places, a key factor in detecting the voting irregularities that often mar elections in the Philippines.

The differences between the two sides go beyond a dispute over party affiliation, however. Many of Aquino's supporters mistrust the Laurel camp as traditional politicians schooled in the Marcos style of government and merely awaiting their turn in power. Laurel and some of his top aides formerly belonged to Marcos' ruling party.