Philippine President Ferdinand Marcos has met recently with two of his most vehement critics and is reportedly considering concessions designed to ease criticism of his one-man rule.

Sources within the organized opposition say Marcos appears ready to release from prison four prominent opposition political candidates. They were jailed for leading a protest march two days after they polled about a million votes each in an April 7-election for an interim National Assembly.

Opposition sources said Marcos is also considering transfering his leading political opponent, former senator Bchigne Aquino, from a prison cell to house arrest and declaring an end to formal martial law. Withdrawing his 1972 martial law declaration presumably would remove the army's power to arrest and try dissidents but would not end Marcos' power to use the police to silence his opponents and would do nothing to change his power to rule by decree under a newly approved constitution.

The reports of possible concessions by Marcos came after meetings between the president and two of his leading opponents, former senator Lorenzo Tanada and attorney Juan T. David. Opposition sources suggest Marcos is looking for a way to high-light the convening of a new National Assembly on independence day June 12, and also to forestall a cut in military aid to his government now being considered by the U.S. Congress.

Under a new constitution and amendments approved by national referendum since Marcos imposed one-man, martial-law rule in 1972, the president can make laws on his own even after the National Assembly convenes if he thinks the situation warrants it. Marcos has portrayed the creation of the assembly asn an important step toward renewal of representative democracy, however, and seems anxious to convince his critics that he sincerely wants to loosen the reins of power.

Some opponents suggest he also wants to undercut the publicity he expects will be given soon in the United States to one of his most outspoken critics, attorney and former assembly candidate Charito Planas. Planas has been sought by police on subversion charges since election day. She reportedly has rescaped from the Philippines and is expected to arrive in the United States soon.

She reportedly reached Malaysia by boat and received funds for her trip to the United States from the U.N. High Commission on Refugees, which has helped a few other political refugees from the Philippines as well as thousands of refugees from Vietnam.

Opposition sources said that David, who once worked as an attorney for Marcos before he became president in 1965, has met with the president three times in recent weeks. Marcos had jailed David's son, a Manila journalist, at the beginning of martial law. The attorney, now in his 70s, had sharply criticized the president while representing one of the defendants in a celebrated murder and subversion trial which also involved ex-senator Aquino. David also ran unsuccessfully for the assembly as an anti-Marcos candidate.

Tanada, 79, who served as campaign manager for the losing anti-Marcos slate in Manial during the National Assembly campaign was himself jailed for helping lead the protest march two days after the election. He was released later. Aquino reportedly wrote to Marcos suggesting he meet with Tanada to try to ease the tensions of the post-election period. Tanada, however, reportedly refused the presidents first call for a meeting and did not consent to join David in his talks with Marcos until Tuesday.

David said yesterday that what transpired at the meeting is "still confidential. Just wait for results." He said he argued that further Marcos crack-downs on his democratic opponents would only strengthen the more radical underground left and the Communist Party.

"It would be better for the people to be represented by a legitimate opposition," he said.

The anti-Marcos, assembly candidates due to be freed, according to the opposition sources, are former senator Francisco Rodrigo, attorney Teofisto Guingona, law professor Aquilino Pimentel Jr. and businessman Ernesto Rondon. Two other jailed campaign leaders would also be released, the sources said, but a priest, the Rev. Archie Entengan, whom Marcos considers too outspokenly radical, would remain in jail.