At least 34 persons were arrested and three were slightly injured, police said, as tens of thousands of Filipinos demonstrated in Manila and across the Philippines today to mark the 13th anniversary of the declaration of martial law.

Most of the incidents took place during a two-hour barrage of noise tonight in the streets of Manila to protest the continued rule of President Ferdinand Marcos. Martial law, which lasted more than eight years, was lifted in 1981, but Marcos retains vast powers.

Manila's district police chief, Brig. Gen. Narciso Cabrera, said a woman suffered a grazing gunshot wound. A fireman and a police captain also were reported hurt.

The left-wing Bayan alliance, which spearheaded the noise barrage, charged that the military tried to raid its headquarters late tonight. Lawyer Procopio Beltran Jr. said three carloads of plainclothes police unsuccessfully tried to get into the deserted office and fired one shot into the air before leaving.

Reports from the provinces indicated there were no major incidents.

Yesterday, soldiers opened fire on antigovernment demonstrators in Escalante, a town in the economically depressed province of Negros Occidental. Police confirmed 16 dead in the shooting, although radio reports put the death toll as high as 20.

Lt. Gen. Fidel Ramos, the armed forces chief of staff, defended the shootings in a television interview today. Ramos said it was "an unfortunate incident" and added that he had sent a team to investigate. He blamed Communists for starting the 30-minute gun battle.

In Manila, separate peaceful rallies were held by both moderate and left-wing groups. The combined crowd of 12,000 demonstrated at two points leading to the presidential palace, which was ringed by barbed wire, more than 2,000 troops and a dozen fire trucks.

Earlier, the moderate opposition held a mock trial, convicting Marcos and his wife Imelda of alleged crimes before a crowd of 5,000.