Manila — As concerns about his health and grasp of political reality grow, President Ferdinand Marcos is under heavy pressure to clarify the dangerously hazy issue of succession.
The President seems to be trying to maintain maximum leeway in the choice of a successor. His opponents, who include leading businessmen and ranking members of the President's own political machine, the KBL (Tagalog initials for the New Society Movement), feel this approach is a recipe for chaos.
They stress that the top priority since the Aug. 21 assassination of Benigno Aquino - which aggravated political uncertainty here and precipitated a financial crisis - is to restore foreign confidence in the country's prostrate economy.
The only way to even begin to do this, they say, is to have a clear-cut succession mechanism that ensures a swift transfer of power.
Many of them suspect the President's desire to keep things vague masks a plan to have his wife, Imelda, succeed him.
''And that,'' a senior executive warned, ''could finish off the economy.'' Most fear that any fumbling or confusion in the transfer of power could lead to a military takeover.
''The slightest hiatus in the succession system,'' a Cabinet minister warned, ''will strongly tempt certain people in the armed forces.'' The minister refused to say who might be tempted.
The last time President Marcos took the oath of office was in 1981 for a six-year term under rules of the parliamentary government he has created since 1972. An executive committee has been established to ensure a smooth succession, should anything happen to Marcos. The concessions announced earlier this month - elections for vice-president in 1987, the appointment of the 73-year-old national assembly speaker, Querube Makalintal, as interim successor, and the resignation of Mrs. Marcos from the executive committee - are unlikely to relieve the pressure for change in the succession rules.
First, the denial of political ambitions that accompanied Mrs. Marcos's resignation from the executive committee will probably not be taken at face value: Such disclaimers have been scattered regularly throughout her political career and have often been the prelude to the reassumption of a major position. Moreover, the committee she resigned from had just ceased to have any function.
Second, many of those who are demanding a new succession system fear that the President will not live until 1987. And third, many of the government's strongest critics in the business community are saying openly that, even if the President survives until then, the economy will not.
Leading the move for change are Emmanuel Pelaez, a member of the executive committee and an important KBL boss from the southern Philippines, and assemblyman Arturo Tolentino, another KBL leader and one of the country's top constitutional lawyers.
Mr. Pelaez is pushing for a constitutional amendment that would give Prime Minister Cesar Virata powers to rule as acting president should anything happen to Mr. Marcos. Mr. Tolentino wants to revive the office of vice-president. Both men want to enact changes in the succession rules fast: Tolentino wants to see vice-presidential elections next May; Pelaez simply says he would like constitutional changes as soon as possible.
They are supported by much of the business community. Many businessmen say they would prefer the President to resign but do not feel he will do so, and have thus opted for a clear-cut succession procedure as the minimum prerequisite for restoring confidence in the economy.
''It's simple,'' said Jaime Ongpin, president of the giant Benguet Mining Corporation, ''we are asking foreign bankers to put in between $1.5 billion and will be running the country when our notes come due?' They want a categorical assurance on the succession.''
The moves are receiving discreet support from other quarters: from some Cabinet ministers, who are privately dismayed at the President's apparent physical decline; from the American Embassy, which has been quietly urging the President to clarify the succession, and probably from Prime Minister Virata himself.
Mr. Marcos's handling of the debate seems to have strengthened doubts about his health and political awareness. His defense of his position has been hesitant, and his concessions have come too little and too late.
At first he maintained his support for the executive committee, created in 1981, reportedly at the urging of the United States and the International Monetary Fund (IMF) to provide interim leadership should the President die or be incapacitated. The 10 members of the body, however, are all KBL stalwarts, and some probably have presidential ambitions.
''The President kept saying, 'Give the committee a chance,' '' said Tolentino. ''He just would not admit that it was fertile ground for a power struggle.''
Then the President changed his mind. On Oct. 31 he announced a clarification: If anything happened to him, the prime minister - ''whoever he is'' - would take over. The clarification may have been aimed at an IMF team in Manila at the time to discuss a vital standby agreement. The team was persistently rumored to have expressed concern about the succession question.
Instead the President's move caused an uproar. The prime minister can be changed by presidential whim, or by a vote of no-confidence in the KBL-dominated National Assembly. And the clarification hinted at broad powers for the KBL secretary-general, a post Mrs. Marcos seems interested in.
Tolentino denounced the announcement as ''not only unconstitutional but extremely dangerous.'' If the prime minister's authority was challenged by other executive committee members, he said, ''this country may be plunged into turmoil.''
''What a boo-boo,'' said an executive committee member, referring to the clarification. ''If Marcos dies tomorrow, we'll all be in the Supreme Court trying to work out who's in charge. Who's advising the guy these days?''
Since the President's annoucement, he has been arguing forcefully, but according to one of his interlocutors not very cogently, against the vice-presidency.
This lack of cogency - from a man who was one of the top lawyers of his generation - is spurring his critics to tie him down quickly to a succession formula. The fact that they have won a partial victory in recent weeks will probably make them push all the harder.