Philippine President Ferdinand Marcos, apparently responding to intense criticism from the Reagan administration and Congress, announced yesterday that he will call a "snap" presidential election within the next three months to settle charges at home and abroad that he is no longer fit to rule.

"I understand the opposition has been asking for an election. In answer to their request I announce that I am ready to call a snap election, perhaps earlier than eight months, perhaps in three months or less than that," he said in a television interview.

Marcos said he thought it was time to put an end to the "childish claims" about his loss of popularity and to settle the issue once and for all by calling a special election "right now, say give everybody 60 days to campaign and to bring the issues to the people."

He insisted that there were no catches to his offer, other than his need to obtain the approval of the legislature, which his party controls. He said that anyone who wanted to run against him could do so, including Corazon (Cory) Aquino, the wife of slain opposition leader Benigno Aquino. Marcos said he would invite members of Congress to observe the voting and to see that charges of fraud in past presidential elections were just "sour grapes" and "a publicity stunt" by his opposition.

His surprise announcement of a special presidential election well ahead of the next scheduled one in May 1987 represents a turnabout from his decision this summer.

It follows sharp criticism of his leadership by administration officials and Congress and visits by high-level U.S. emissaries, the latest by Sen. Paul Laxalt (R-Nev.), warning him that unless he makes sweeping reforms he stands to lose all U.S. support. Sen. David F. Durenberger (R-Minn.), chairman of the Senate Select Committee on Intelligence, said Friday he thought Marcos was incapable of the reforms required and should give up his office.

Neither the State Department nor the White House had any comment on Marcos' announcement, which came during an interview on ABC News' "This Week with David Brinkley."

Rep. Stephen J. Solarz (D-N.Y.), chairman of the House Foreign Affairs subcommittee on Asia and a persistent critic of Marcos, called the announcement "potentially a very significant development." But Solarz warned that "a genuinely free and fair election would be essential" and that "a fraudulent election would be worse than none at all."

After the interview, Marcos was reported to have told ABC News producer Bill Thomas that the election might be held Jan. 17, the anniversary of the 1981 ending of eight years of martial law. A decision would be made next week, Thomas quoted Marcos as saying.

Marcos also hinted that he may be ready to reach a compromise over the fate of Gen. Fabian Ver, the Philippine armed forces chief of staff who was suspended from his duties after being implicated in the murder of Aquino in August 1983.

Marcos, who has promised to reinstate Ver if he is acquitted of charges in the Aquino case, said, "I never promised how long he was going to stay."

Marcos said he would call together the military officer corps to discuss a sweeping reorganization of the armed forces to avoid "a firestorm" of protest in the U.S. Congress. "It's due anyway," he said.

Laxalt, who was interviewed first on the program with Marcos, warned that Ver's reinstatement for "any extended period of time could well cause a firestorm here in Congress."

"It's that sort of simple thing that will cause the Congress to react and react violently," he said.

Laxalt indicated he had warned Marcos during their meeting in mid-October of likely adverse congressional reaction to a Ver reinstatement. The senator also said he told Marcos of President Reagan's deep concern about the Philippines, where a communist-led insurgency has made considerable headway amid the country's economic crisis.

Laxalt said Marcos had read "very carefully" a three- or four-page handwritten letter from Reagan he had delivered and that it was his impression the Philippine leader was "touched" by it.

"He looked up at me and said, 'Senator, I don't mean at all to add to the burdens of this great president,' " Laxalt said.

In the interview, Marcos sought to link progress in the government's campaign against the communist insurgency to his country's economic crisis in an apparent bid to gain the sympathy of the United States and the International Monetary Fund. The IMF has held up more than $450 million in loans to the Marcos government, pending an agreement on economic reforms.

Regarding the "snap" election, Marcos said he would ask the National Assembly to approve an amendment to the pending election code -- which already provides for special elections in case of a presidential death, resignation, disability or removal from office -- to allow a president "to bring a fundamental issue to the people" and vote on it.

He seemed to be indicating this procedure -- similar to a referendum -- would take the place of the current requirement for the president to resign from office at the start of the 60-day campaign, during which time the speaker of the National Assembly is supposed to become acting president.

Marcos said he thought he could convince the Assembly to accept his amendment because his party controls two-thirds of the seats.