Philippine President Ferdinand Marcos threatened today to "exercise to the limit" his powers to "prevent turmoil" and thwart what he said were opposition plans to destabilize his government through civil disobedience and general strikes.

Marcos did not say what specific powers he would employ or if he would invoke martial law, as he did from 1972 to 1981.

After receiving the credentials of the new Soviet ambassador, the first envoy of a major power to congratulate Marcos on his reelection, Marcos chastised foreign observers who monitored the Feb. 7 election and warned against "interference in the internal affairs of our people." He apparently was referring to U.S. and other observers who have condemned the election as fraudulent.

His comments came as opposition leader Corazon Aquino took her postelection campaign for the presidency to a town in Pampanga Province, next to the largest U.S. Air Force base outside the United States, and publicly warned Washington that she would not accept reconciliation with Marcos or a new election. Marcos has said that he would not accept Aquino as a member of his Cabinet.

In a related development, U.S. presidential envoy Philip C. Habib today denied through a U.S. Embassy spokesman that he had warned Marcos that he must institute democratic reforms and share power with the opposition or risk losing U.S. aid. In a report yesterday from Washington, unidentified administration officials were quoted as saying that Habib delivered such a warning.

Today's developments came as a three-day-old boycott called by Aquino began to take hold here, hurting businesses associated with Marcos.

In her visit to the town of Angeles, next to Clark Air Base, Aquino told about 30,000 people that she would press ahead with her nonviolent struggle against Marcos until she brings down his government. She urged supporters to enforce a boycott announced Sunday against businesses, news media and banks controlled by the government or those the opposition considers presidential "cronies."

She said the boycott would be expanded next week, and she called for a nationwide one-day strike -- including a boycott of school classes -- for the day after Marcos' inauguration, scheduled for Feb. 25.

The rally, similar to the 53-year-old widow's election stumping, marked the start of her campaign to popularize the opposition boycott and other anti-Marcos measures in the provinces. She said she planned to tour 10 major cities to spread the campaign and press her claim that she is the legitimately elected president.

As aircraft from nearby Clark Air Base periodically thundered overhead, Aquino warned that she would no longer meet with U.S. envoy Habib if he were pushing cooperation with the Marcos government. She also ruled out any new presidential election, in apparent response to suggestions of some U.S. congressmen.

Marcos has offered Aquino a position in a yet-to-be formed Council of State, but it is not clear what its role, or hers, would be.

"If you have come here to tell me to cooperate, don't visit me anymore," she said of Habib during the rally. Aquino, her running mate, Salvador Laurel, and several advisers conferred with Habib for an hour Monday. Aquino aides who participated said afterward that no reconciliation deal was proposed.

Earlier Monday, Habib also met for two hours with Marcos, including one hour by themselves, at the Malacanang presidential palace. Marcos said afterward that Habib had told him that he was here only to "make observations" for Reagan and that the United States "was not interested in any way in telling us how to run our affairs."

In denying the reports from Washington, a U.S. Embassy spokesman said today: "There is no basis in fact for those statements."

As in past diplomatic missions, Habib has refused to make any comment to reporters on his activities or even to disclose his schedule. The government reported today that he conferred with Marcos' running mate, Arturo Tolentino, who called the meeting fruitful.

Marcos, Tolentino and leaders of the ruling New Society Movement party gathered for a three-hour caucus at the palace late last night to plot strategies for countering an opposition civil disobedience campaign, the palace reported today. Marcos urged unity and national reconciliation following the disputed election but warned that he would "enforce the law" if planned general strikes paralyzed transportation and other public utilities, a palace statement said.

"I will exercise to the limit the provisions of the law and the constitution to prevent turmoil," it quoted Marcos as saying. He told the caucus that he has "certain powers that can dismantle the machineries of civil disobedience." The statement did not elaborate.

The Malacanang palace also reported that Marcos, after accepting the credentials of new Soviet Ambassador Vadim I. Shabalin, said the Philippines would now encourage expanded trade ties with Moscow.

The question of international recognition of Marcos' reelection after charges of fraud and violence has begun to surface as a local issue. Opposition newspapers reported today that New Zealand Prime Minister David Lange had sent word through his embassy here that he would not be messaging congratulations to Marcos. News agencies reported from Kuala Lumpur that two Malaysian opposition parties had asked Prime Minister Mahathir Mohammed not to recognize Marcos as the Philippines' president because of the alleged electoral fraud.

News agencies also reported that Spain and West Germany recalled their ambassadors from Manila today for consultations.

In her speech today, Aquino said she would ask friendly governments not to recognize Marcos.