President Ferdinand Marcos and his ruling New Society Movement party threatened today to call a snap presidential election and dissolve the National Assembly if opposition legislators push ahead with a resolution to impeach him in connection with a series of financial scandals.

The Malacanang presidential palace said in a press release after a late-night caucus that Marcos and ruling party representatives had "seriously discussed" holding an election for president and vice president "within the year" and dissolving the assembly after mid-November. The statement said the conferees deferred a final decision on the proposals until the opposition legislators take further action on the impeachment resolution.

Citing "efforts at harassment and attempts to discredit the presidency," Marcos expressed a preference for seeking "a new mandate from the people" well before his current six-year term expires in 1987, the palace statement said. The president accused the opposition of trying to block an economic recovery program and a "quick solution" to the problem of a Communist insurgency.

A spokesman for the president said that although an impeachment resolution has no chance of passing in the National Assembly, which is controlled by the ruling party with a 2-to-1 majority, it "might erode the confidence of the people in the ability of the president to lead" and undermine his standing with foreign governments and creditors.

A leading opposition member of the assembly, Homobono Adaza, said the anti-Marcos forces will go ahead with the impeachment resolution despite the threat to dissolve parliament, which he called a "bluff." He said the opposition welcomes an early presidential election, a proposal that he claims resulted from an "ultimatum" to Marcos from the Reagan administration to seek a new mandate.

Marcos, who has been in power for 20 years, was elected twice to four-year terms in the 1960s. He declared martial law in 1972 before the end of his second and final term but lifted it in 1981 to run for president again under a new constitution that allows unlimited six-year terms in a parliamentary system. However, the 1981 presidential election was boycotted by most opposition groups, which, in effect, spoiled Marcos' bid for new electoral legitimacy.

Last week, as Marcos opened a new session of the National Assembly, which was elected in May 1984, opposition legislators distributed a resolution demanding his impeachment on grounds of "economic treason." The resolution cited alleged financial irregularities including massive overseas investments by Marcos' wife, Imelda, top government officials and presidential friends in what is being called the "hidden wealth" scandal.

According to Adaza, a cosponsor of the resolution, it now has 53 signatures and will be submitted by the end of next week. He said the opposition needs 40 votes, or one-fifth of the 200-seat legislature, to initiate impeachment proceedings and to send the resolution to a committee.

Although the resolution is likely to remain bottled up in the committee, Adaza said, the procedure would prevent the dissolution of the assembly. Under the new constitution, the president cannot dissolve the legislature within 18 months of the beginning or end of the parliamentary term or if impeachment proceedings are under way.

Adaza said that in raising the prospect of a snap election, Marcos apparently is gambling on disunity in opposition ranks that would produce more than one opposition candidate and split the vote.