Philippine opposition leader Jovito Salonga returned today from nearly four years of voluntary exile amid unusually tight security and said he favored removing U.S. military bases from the Philippines.

The former senator, 64, said he was returning home from the United States to help unify the opposition and rebuild democracy in the Philippines.

The country, he said, yearned to see a vigorous, united opposition present an alternative to the rule of President Ferdinand Marcos. He warned that more than eight years of martial law under Marcos had taught Filipinos a lesson. "We do not deserve freedom unless we fight for it, suffer for it and even die for it," he said.

Salonga, who did not rule out the possibility of running for president in 1987 if drafted, said he would serve in whatever role he might be assigned.

The government dropped subversion charges against Salonga in order to smooth his return. He was charged with trying to kill Marcos and other top Philippine leaders.

Salonga said the dropping of the charges "constituted the most authoritative admission that for four years my family and I were unjustly smeared, persecuted and hounded."

His supporters arranged for tight security for his arrival. It was at the Manila airport that Marcos' chief political rival, Benigno Aquino Jr., was shot dead moments after he stepped off a plane in August 1983.

Salonga was escorted from Hong Kong -- the last leg of his trip -- by 15 colleagues including former senators Lorenzo Tanada, Jose Diokno and Agapito Aquino, younger brother of Benigno Aquino.

Corazon Aquino, widow of the late senator, and assembly member Eva Estrada Kalaw were among the 300 journalists and supporters who met Salonga at the airport.

Salonga was questioned at length about the removal of U.S. bases and the legalization of the Communist Party of the Philippines -- two controversial points that nine potential presidential candidates, including Salonga, have drawn up as part of a unity pact among some representatives of the Philippine opposition.

On the issue of the U.S. bases, Salonga said: "The removal of the American bases in the Philippines is not an earth-shaking demand, not an extraordinary demand." The bases agreement will expire in 1991, and it will take another five to six years to dismantle them, he added.

On the legalization of the Communist Party of the Philippines, Salonga said: "They must lay down their arms, provided they have the trust of the government. The reason they take up arms is . . . they have no trust in the present government."