Vice President Mondale has promised asylum in the United States to a Philippine dissident now hiding from police who seek her arrest on subversion charges, according to martial law opponents who saw Mondale here.

The fugitive dissident, attorney Charito Planas, must first find a way to get out of the country undetected, because Mondale offered no help until she reached American soil, said a source who presented her case to Mondale.

Travel restrictions on both public and private critics of President Ferdinand Marcos' one-man rule have become so tight that even Jaime Cardinal Sin, the leading prelate in this heavily Roman Catholic country, was briefly delayed in boarding a flight to Rome Sunday because his name was on a travel blacklist.

The promise of asylum for Planas came during a series of meetings Mondale had here May 3 with Marcos opponents he had asked to see in order to assess reports of human rights violations. Mondale's press secretary, Albert Eisele, said in a telephone interview this week that Planas' name came up during the afternoon "but since the meetings were private I can't go into the details."

Planas received almost 1 million votes out of about 3.1 million counted in Manila in an April 7 election for seats in a new, but relatively powerless, interim National Assembly. She was one of 21 anti-Marcos slate candidates who took about 40 per cent of the Manila vote and was perhaps the most outspokenly critical of Marcos and his wife, Imelda, who led the winning assembly ticket in the capital.

Government security officers raided Planas' house here on election day and said they found an illegal automatic rifle and "subversive literature." Marcos said that Planas, a former martial law detainee, had sheltered several members of the Communist New People's Army. She was not at home when the police arrived and is reported to have been in hiding in the Manila area ever since.

Any American assistance to Planas would add one more irritant to a somewhat tense U.S.-Philippines relations that seemed improved by Mondale's low-key approach to the human rights issue during his two-day visit here.

U.S. officials reportedly helped Joel Rocamora, a Philippine university professor with an American wife, leave the country two years ago when he was hiding from police. U.S. Embassy intervention helped bring the release of another Marcos opponent, slum organizer Trinidad Herrera, a year ago after she had been allegedly tourtured.

But a U.S. Embassy spokesman replied "no comment" Wednesday when asked if Planas was getting any American help to get out of the country. A spokesman for the Philippine Department of Foreign Affairs, when asked if the U.S. government was seeking safe passage for Planas, said "as far as I know, no approach has been made."

In August, Marcos lifted a general ban on overseas travel without specific government approval, but shortly after the April 7 election immigration authorities compiled a new travel blacklist of about 460 Marcos opponents. A copy of one such list made available to The Washington Post included the name of Planas and apparently every other anti-Marcos candidate in the election, but there was surprise when Cardinal Sin's name appeared on another version of the list.

An unusually strong statement issued by Catholic clergy in Manila Wednesday protested the cardinal's being detained briefly at the airport Sunday and only allowed to board his flight after a telephone call to the presidential palace. Sin has rarely spoken out against Marcos although has reportedly been critical of martial law in private conversations with the president and with Mondale.

"If a man of his status is not immune to harassment, what of ordinary citizens like us," said the statement by the Manila clergy about Sin.

Marcos reacted by ordering an apology to the cardinal. A government statement Friday blamed the incident on a "low-ranking military subordinate" suffering from "misinformation."

Four anti-Marcos assembly candidates were jailed two days after the election for leading a peaceful but illegal protest march. The leading opposition vote-getter, former Sen. Benigno Aquino, has been in jail on murder, subversion and arms possession charges since 1972. Slum organizer Herrera, also an assembly candidate, is now also being sought by police on subversion charges and, like Planas, she is reported to be hiding in the Manila area.

Opposition sources said they did not press Herrera's case with Mondale because they feel the earlier interest shown in her by the U.S. Embassy will save her from harsh treatment in the future.