There is widespread belief in Manila that the Philippine government was involved, in one way or another, in the assassination of leading political opposition leader Benigno S. Aquino Jr.
Rumors swept the capital Monday as a power blackout afflicted the entire city most of the day.
Monday evening President Ferdinand Marcos appeared on television to deny rumors of a coup, a reimposition of martial law, or public panic.
The President said that the rumors were orchestrated by members of the opposition who were using the ''spite and anger'' that is natural after the killing of a man like Mr. Aquino. The President also suggested that several high-ranking officials of other governments, which he did not name, had helped Aquino return to the Philippines.
The President expressed particular concern at rumors implicating his wife, Imelda, in the killing. Mrs. Marcos, he said, had in fact prevailed on him to allow Aquino to go to the United States for medical treatment in 1980.
The President did not elaborate on the alleged insinuations, but may have been referring to two conversations that opposition leader Salvador Laurel reportedly had with Mrs. Marcos in the National Assembly. The first took place Aug. 2, former Senator Laurel told The Christian Science Monitor.
In the presence of several other people, Mr. Laurel says he jokingly asked Mrs. Marcos if she would like to welcome Mr. Aquino when he returns. Mrs. Marcos answered with words to the effect that if Mr. Aquino comes back, he will be killed.
On Aug. 15, Mr. Laurel said he told Mrs. Marcos that Aquino would return on the 21st. Mrs. Marcos replied this was impossible. And, Laurel added, she said Aquino ''could or will be killed.''
Mr. Laurel says he could not judge from the tone of voice how Mrs. Marcos wanted the comments to be interpreted. But he assumed they referred to the government's previous warnings of alleged death threats by Aquino's enemies.
(In referring to President Reagan's scheduled trip to Manila later this year, White House spokesman Larry Speakes told reporters Sunday, ''There are no changed plans for the trip to the Philippines.'' Asked about security for Mr. Reagan during the visit, Mr. Speakes said, ''There are no qualms.'' New York Democratic Rep. Stephen Solarz, chairman of the House Subcommittee on East Asian and Pacific Affairs, told Reuters in Bangkok that President Reagan should not make the trip, ''If it should turn out that there is strong reason to believe that the Marcos government was involved in this dastardly deed.'')
Marcos said the assassin had not yet been identified, but added that the man was probably a professional killer. The President suggested the killing was the work of the outlawed Communist Party. The communists, he said, felt that Aquino had liquidated some of their members whom Aquino had used for unspecified activities of his own in the past. In the past the government has accused Aquino himself of being a communist.
By doing so, he said, the communists had ''shot two birds with one stone'' - they had also embarrassed the government.
Marcos repeated his shock at the ''dastardly'' murder of Aquino. But, he said , the recent attempts on the life of Pope John Paul II and President Reagan showed that it was impossible to protect a public official from a determined assassin.
Marcos criticized foreign journalists for ''rushing'' to join the Aquino plane from Taipei. (Landing rights for China Airways of Taiwan have been suspended in the Philippines.) He criticized the foreign press for spreading ''venom'' against the Philippine government and himself.
Marcos's unexpected appearance on television follows a day of government silence and wild rumors in the streets. Rumors included claims that martial law had been reimposed, that there had been a coup, and that there was student unrest in the state-run University of the Philippines.
The President's health was difficult to judge from his TV appearance. Though he derided reports that he was ill, recent visitors have said that he had difficulties getting into and out of a chair. A recent announcement that Marcos planned to seclude himself for several weeks to write a book, or that the air conditioning at the presidential palace was being repaired - thus preventing official visitors from calling - have led to renewed speculating that he was seriously ill.
In the streets, people reacted to the Aquino killing with scepticism or nervousness. Many express doubts about the official version of Aquino's killing - that he was shot down by a single gunman, and are worried by the possible consequences of the killing.
The powercut was widely rumored to be sabotage. Investigations into the cut were said by the government to be continuing. Reports indicated that some government offices had closed early as reports of the reimposition of martial law had begun to spread around the capital.
While a few Filipinos were unwilling to say anything about the Aquino killing , and avoided the question with a shy smile, most were quite forthcoming.
''It was an inside job,'' said a man who is a member of a Barangay Brigade, a government-sponsored community organization. ''The papers had pictures showing how strong security was at the airport.''
''Only a magician could have got into the airport with a gun,'' said an office worker. Others expressed cynicism about the outcome of the murder investigation. ''They won't discover anything,'' said a taxi driver, ''because the assassins and the investigators work for the same people.'' He refused to elaborate.
The coroner who inspected Aquino's body reported that the killing was done by a gunshot some two inches from the head. The official report claimed the distance was ''less than'' 18 inches. This has led to speculation that the killer was allowed easy access to Aquino.
Aquino's funeral may be held on Monday, Aug. 28, some sources say.