Filipino exiles who oppose President Ferdinand Marcos' martial law government are stepping up their efforts to presuade the United States to halt military assistance to the Philippines.

The Movement for a Free Philippines has three new members.

Two of them, Gerald Jumat and Benjamin Maynigo, escaped from the Philippines last October and arrived in the United States March 4 as political refugees.

They had worked in Zamboanga, a major town on the southern island of Mindanao where the government has been fighting a Moslem rebellion.

In a recent interview Jumat, who was a staff aide to Rear Adm. Romolo Espaldon, the commander in the region, said the government had broken so many promises to the Moslems that he believes the South will be unstable as long as Marcos is in power.

One of the factors that convinced him to flee, Jumat said, was the loss of credibility suffered by all local officials as a result of the broken promises.

U.S. military aid, Jumat said, is used against the Moslems in the South and should be halted. Jumat was raised a Moslem and converted to Catholicism.

The Carter administration has proposed $19.6 million in grant military aid, $800,000 in grants for training and $20 million in military sales credits for the Philippines in fiscal year 1978.

The third new recruit to the movement - formed shortly after Marcos declared martial law in September, 1972 - is Bishop Manuel P. del Rosario, the highest-ranking Catholic churchman to join.

The bishop left the Philippines in July, 1975, after denouncing the first referendum Marcos held to ratify martial law. He call the January referendum a fraud and advocated boycotting it, despite a government ban on such criticism.

When he heard that some others who urged a boycott were being arrested, del Rosario asked the papal nuncio to intervene to request permission for him to travel to the United States for medical attention. The bishop's right side has been paralyzed since he suffered a stroke 11 years ago.

In a recent interview, del Rosario said Marcos is trying to weaken the church because of opposition to his government by Catholics.

He said he only recently decided to become active in the exile opposition movement because he wanted to wait until he was granted permanent resident alien status in this country.

Last December, del Rosario contacted the president of the movement, Raul Manglapus, and expects to work from his Toledo, Ohio, base to organize opposition to U.S. support for Marcos. There are about 400,000 Filipinos in the United States, according to the official figures, but the number is known to be considerably higher.