An executive of a leading Filipino-American newspaper opposed to Philippine President Ferdinand Marcos was shot to death today after receiving a death-threat letter calling the paper "a disgrace to the Filipino community in the U.S."

Police said several shots were heard in the bedroom of Oscar Salvatierra, 41, a naturalized American who had spoken out against Marcos. His body was found there this morning in a hilly neighborhood of suburban Glendale, Calif., they said.

Police and FBI agents said they have no immediate suspects but indicated that they will investigate the possibility that Salvatierra was the victim of recent efforts to intimidate anti-Marcos activists in this country.

The Philippine News, published in six weekly English-language editions, circulates about 77,000 copies in the United States and Canada, mostly in California. It is the largest weekly financed by advertising and paid subscriptions circulating among the nearly 1 million U.S. residents of Filipino descent.

Salvatierra was marketing director in the paper's bureau here.

Supporters of Corazon Aquino, declared the loser to Marcos in the bitterly contested Philippines presidential election this month, charged that Marcos agents murdered Salvatierra.

If true, the killing would be the latest of several violent acts by foreign agents against politically active members of growing Asian immigrant communities throughout the western states.

In the News' most recent issue, Salvatierra's name is listed first among those working in the newspaper's Los Angeles bureau. The main headline says, in red letters, "Marcos Stealing Election."

The letter sent to Salvatierra was postmarked Friday in Los Angeles and reached him Tuesday. Composed of words cut from newspapers and magazines and pasted on a sheet of paper, it said:

"Philippine News is a disgrace to the Filipino community in the U.S. Through your paper your unwarranted accusations and lies have attacked your own countrymen. You should be ashamed to call yourselves Filipinos. So for your crimes you are sentenced to death by execution."

On Saturday, before Marcos was declared winner of the Feb. 7 election, Salvatierra told a reporter from Los Angeles television station KNBC:

"I'm afraid there is going to be a lot of killings, a lot of violence. A lot of the opposition leaders will have to be killed or be put in jail to prevent the will of the people from being oppressed."

Steve E. Psinakis, a San Francisco-based Aquino movement leader who acts as a consultant to the News, said Salvatierra was a quiet man who had refrained from expressing strong political feelings until after the 1983 assassination of Sen. Benigno S. Aquino Jr., Corazon Aquino's husband and Marcos' leading political opponent.

Stunned colleagues at Salvatierra's office said his wife, a nurse, was at work and his four children at school when the shooting occurred. Police said they were called by Salvatierra's elderly mother, who speaks no English, after she heard shots in her son's bedroom in the community about 10 miles north of Los Angeles.

"We have been afraid of something like this for a long time. But when it actually happened we were stunned," said Heroico Aguiluz, an attorney for the newspaper. Staffers said an unexploded bomb was found in the office last July 9.

Asked whom he blames for the killing, Aguiliz said, "Marcos."

News staff members said their Los Angeles sales representative, Stan Aragon, had received a letter similar to Salvatierra's before the killing. It said, "You are going to be next."

Sen. Alan Cranston (D-Calif.) issued a statement saying he had been told of the killing by News Publisher Alex Esclamado, who also has received threats. Cranston said he asked FBI Director William H. Webster to investigate "this atrocity" and provide protection for Esclamado, Aragon and their families.

"Mr. Esclamado believes all this is the work of Marcos' agents and intended to intimidate him in ceasing his opposition to the Marcos regime. On the basis of Marcos' behavior in the Philippines, there is even more reason to believe Mr. Esclamado's suspicions are well-founded," Cranston said.

A statement by the Philippine consulate here, read by acting Consul General Leovigildo A. Anolin, deplored Salvatierra's death as an "apparent gangland-style killing," the Los Angeles Times reported.

"For some people to exploit the death of Mr. Salvatierra in an attempt to make political capital out of it is indeed incomprehensible," the statement said. "We sincerely hope that whoever is responsible . . . will be brought before the bar of justice to answer for his dastardly deed."

Pinakis said initial reports of the threat against Salvatierra and his murder parallel the murder of Chinese-American author Henry Liu in Daly City, Calif., in 1984.

A court in Taiwan later ruled that Liu, a critic of the Taiwan government, had been murdered by members of a criminal gang with ties to high officials of the Nationalist Chinese military on Taiwan.

Psinakis also noted that two other U.S. resident Filipinos have been killed and that one had disappeared in the last nine years in incidents in which involvement by Marcos supporters in this country was indicated.

He cited the case of Primitivo Mijares, a former Marcos censor who broke with the president and told a U.S. congressional committee in 1975 that Marcos had secretly instigated violence that led to his 1972 declaration of martial law.

Mijares was last seen Jan. 7, 1977, in San Francisco with a man identified as a Philippine intelligence agent. A letter Mijares sent from Honolulu the next day said he was returning to the Philippines but expected danger.

Psinakis said congressional investigations indicate that Philippine military officers assigned to U.S. consulates are in touch with Filipino criminals and have received orders to harass Marcos opponents.