THE Philippines' two political widows, Corazon Aquino and Imelda Marcos, are locked in an escalating battle of wits.Last week, Mrs. Aquino fired the first salvo by announcing that the widow of the late President Ferdinand Marcos could return from exile in the United States, but only without her husband's remains. The government action elated - then stunned - Mrs. Marcos. Anxious to bury her husband at home, she initially declared her readiness to go home and face trial. But a day later, when the government cagily granted a visa that would not allow her to leave the Philippines, the widow angrily denounced the conditions and suggested she would not be going anywhere soon. The Aquino government warned that it would proceed with a corruption investigation against Mrs. Marcos and her children even if she waived her right to come home. Aquino, who blames former President Marcos for the 1983 assassination of her husband, opposition leader Benigno Aquino, is concerned that returning Marcos' body will trigger political unrest. Despite battered reputations, both Aquino and Marcos continue to be political keystones in the Philippines. Mrs. Aquino, who has survived seven coup attempts, including some linked to Marcos and his followers, insists she will not run again. Still, her endorsement will be crucial to the success of any anti-Marcos candidate. Some analysts say Imelda's return could work in Aquino's favor and divide the political opposition trying to forge a united front against the Aquino candidate. "Imelda's role will be that of a spoiler, but the problems would be more with the opposition than with the government," says Amando Doronila, a Manila newspaper editor. "She was not liked even when Marcos was alive. They blame Imelda for the popularity of Aquino."