El Salvador's leftist guerrillas yesterday vowed as expected to continue their fight following last Sunday's election. They also charged that the failure to produce a clear winner was forcing the United States to interfere more in Salvadoran politics.

The Farabundo Marti National Liberation Front, the umbrella group uniting the various guerrilla factions, and its political arm, the Democratic Revolutionary Front, issued a statement dismissing the election as a fraud and repeating their offer to negotiate with the Salvadoran government.

"The popular war will continue, and our disposition to begin negotiations to achieve peace remains standing before, during and after the elections," the statement, released by guerrilla representatives in Washington, said.

In West Germany, however, Democratic Revolutionary Front leader Guillermo Ungo said the guerrillas would not negotiate with a government headed by the far-right Nationalist Republican Alliance, which placed second in the voting.

"It is foolish to believe that you can have a democratic fascist government," Ungo was quoted as saying by The Associated Press.

The guerrillas boasted in their statement that they had delivered "important blows" against the Army during the voting. But they did not explain why their attacks failed to prevent the election, as they had predicted beforehand.

The guerrillas had rejected the election all along as a U.S.-inspired propaganda ploy and said the ballot would not affect their policies. Noting that U.S. Ambassador Deane R. Hinton met Monday with Salvadoran party leaders after no party won an absolute majority, the guerrillas said: "The people of El Salvador ask: What is the meaning of elections, if the day after elections the politicians meet in the house of the Yankee representative to split the pie?"

The front charged that "manipulation in the election results has been evident" and accused the government of forcing people to vote.