A series of actions by federal officials, including a midnight raid on the San Francisco home of a leading opponent of Philippine President Ferdinand Marcos, have aroused fears of a major crackdown on anti-Marcos activities among the estimated 800,000 people of Philippine descent in this country.

U.S. officials say there is no attempt on the part of the U.S. government to frustrate dissent, but Philippine dissidents are concerned that the Reagan administration is involved in an organized campaign to shore up Marcos' one-man rule.

They point to a visit to Manila by Secretary of State Alexander M. Haig Jr., complimentary remarks about Marcos by Vice President Bush and a U.S.-Philippine extradition treaty signed in November as further signs of strong new American support for Marcos.

This is a sharp change from the Carter administration, which was a frequent critic of human rights policies in the Philippines.

"There has been definitely a great effort between the Reagan administration and the Marcos regime to repress any resistance here," said Steve Psinakis, a journalist and anti-Marcos activist whose home was raided by about 20 federal agents and two bomb-sniffing dogs the night of Sept. 17.

During the three-hour raid, in which agents unwrapped Christmas presents for Psinakis' children, many personal papers were copied or confiscated. If those papers fell into Marcos' hands, they could be used against dissidents in the Philippines, Psinakis said.

Assistant U.S. Attorney William Farmer, who is involved in a federal grand jury investigation in San Francisco into U.S. ties to bombings in the Philippines, indicated in an interview that the search had been based on information that bomb parts and tools might be found at Psinakis' home.

According to a list left by federal agents with Psinakis, no obvious bomb materials were found, but agents did subpoena for grand jury testimony another Marcos critic, Charles Avila, who was at the house at the time.

The federal list said a .22-cal. handgun and a picture of people holding weapons were taken from Avila.

The U.S. investigation grows from bombings in the Philippines in late 1980, including a blast at a Manila convention of the American Society of Travel Agents that injured about 20 persons, including seven Americans.

A revolutionary anti-Marcos group called the April 6 Liberation Movement claimed responsibility for the bombing, but the leading Marcos opponents in the United States have denied involvement with the group.

A U.S. State Department official said the investigation "is not a political effort of any kind. We are looking to uncover violations of U.S. law."

Individuals in this country linked to the bombings could be prosecuted under the U.S. Neutrality Act, which prohibits conspiracy to forcibly overthrow allied governments, or under the Arms Export and Munitions Control Act, which bars the unauthorized export of arms and explosives from the United States.

A key figure in the investigation is Victor Burns Lovely, 36, a naturalized American from the Philippines who was arrested in Manila after being injured in a hotel explosion in 1980.

While in Philippine custody he signed confessions connecting U.S. dissidents, including Psinakis, with the anti-Marcos violence, and U.S. authorities arranged for him to come to San Francisco to testify before the grand jury.

Once he reached the United States, however, his Los Angeles attorney, Jose Lauchengco, said, Lovely disavowed his confessions and said they were forced under torture.

He has refused to testify further to the grand jury and is free on his own recognizance while he appeals a contempt ruling designed to force him to testify.

Lauchengco said he fears that Lovely easily can be returned to the Philippines, where he could suffer further torture, if the U.S. Senate ratifies the extradition treaty signed in November.

Anti-Marcos leaders here said they fear the treaty could be used to extradite several prominent Filipinos wanted on what they call fraudulent charges of murder and other criminal offenses made against them because they oppose Marcos.

The most prominent of these is former Philippine senator Benigno Aquino Jr., now a fellow at Harvard's Center for International Affairs but for years a prisoner in Manila before Marcos freed him in 1980 to seek medical treatment in the United States.

A State Department official said that if the extradition treaty is ratified requests from the Marcos government for the return of Philippine suspects in the United States must be approved by the State Department and the Justice Department.

Requests can be brought if the evidence is not sufficient or the legal system in the country requesting extradition is not thought to meet American standards.

Even with approval from Washington for extradition, a person in danger of extradition may argue before a U.S. judge that the evidence and the legal system of the requesting country should forbid his extradition and he may appeal the case to the U.S. Supreme Court.

A Senate staff member said it is unclear what the chances for the ratification of the extradition treaty are.

A State Department spokesman said persons who have received political asylum in the United States, such as two prominent Marcos opponents whom Psinakis helped make a daring escape from a Manila-area prison in 1977, are not automatically safe from extradition but the fact of receiving asylum would weigh in their favor.

Psinakis is a naturalized American citizen whose wife's family is prominent in anti-Marcos activities. His brother-in-law, Eugenio Lopez, was one of the two wealthy dissidents who escaped in 1977. Psinakis said the search of his house was "mostly civil and polite," but at one point an agent panicked and fired a handgun.

The firing stopped immediately and no one was hurt.

Psinakis said the agents, who kept him and his attorney in one room isolated from the search, apparently went through almost all his files and photocopied several documents.

They also confiscated many personal papers, the contents of two vacuum bags, a piece of metal from a work table, a small screwdriver, batteries, a wire cutter, a knife, a utility kit and the original manuscript of Psinakis' book, "Two Terrorists Meet," which focuses on a five-hour meeting he had in New York with Marcos' wife, Ymelda, in 1980.

Psinakis said he has visited training camps for anti-Marcos guerrillas "outside the United States" in his capacity as a journalist for Philippine-American publications.

Aquino, in a telephone interview, said he had traveled recently to the Middle East to talk with anti-Marcos Moslem leaders.

Psinakis, Aquino, prominent Washington-area anti-Marcos leader Raul F. Manglapus and several other dissident leaders were visited almost simultaneously in March by federal agents asking about the Philippine bombings, but they have denied involvement in any violent acts.

Marcos, elected in 1965 and reelected in 1969, has been plagued by terrorism throughout his administration and in 1972 declared martial law. He lifted martial law earlier this year and won easy reelection as an unopposed candidate in June, but his opponents labeled the election a farce.

He retains sweeping powers to legislate by decree, and can order arrests and indefinite detention of those suspected of crimes involving national security.