Former secretary of state Edmund S. Muskie said yesterday "there's no question" that leftist guerrillas in El Salvador are receiving Cuban arms through Nicaragua under circumstances that could force President Reagan to cut off aid to Nicaragua's revolutionary government.

In an interview with editors of The Washington Post, Muskie charged that Cuban arms and supplies being used in El Salvador's bloody civil war are flowing through Nicaragua "certainly with the knowledge and to some extent the help" of Nicaraguan authorities.

His words marked the first time that someone with recent access to the highest-level U.S. intelligence on Central American publicy has linked the Nicaraguan government to the Cuban-supported guerrillas seeking to win power in El Salvador.

The State Department, which Muskie headed until 10 days ago, has refused to say publicly whether it believes Nicaragua is involved in the Salvadoran conflict. The department's position, as enunciated last week by spokesman William Dyess, is that it is studying the allegations about Nicaragua but has "reached no conclusions."

Since the overthrow of the Somoza regime almost two years ago, Nicaragua has been governed by a junta dominated by the Sandinista Liberation Front, which contains elements that are avowedly Marxist and pro-Cuban. However, former president Carter, seeking to coax Nicaragua toward a moderate, nonaligned position, had pursued a policy of friendship that included winning congressional approval for a $75 million Nicaraguan aid package.

Congressional conservatives attached strings to the legislation, including a requirement that the White House certify that Nicaragua is not aiding guerrillas in other Central American countries. That has focused attention on neighboring El Salvador, where the United States is trying to help a centrist military-civilian coalition consolidate power in the face of violent challenges from left and right.

Muskie said yesterday, "There's no question that if this flow continues with the knowledge of the Nicaraguan government and contrary to the provisions of the legislation which supplied the $75 million, this administration [Reagan's] may be forced to cut off aid to Nicaragua, which could well precipitate a bloodbath in Nicaragua."

Muskie didn't spell out "bloodbath." He apparently was referring to the possibility that economic dislocations caused by a cutoff of U.S. aid could lead to fighting between Nicaragua's Marxist factions and those who want to keep the country out of the Cuban orbit.

Of the $75 million aid package, only $15 million remains undisbursed. The State Department said last week it was holding up this final increment while it completes a study of whether te aid is being used according to the conditions laid down by Congress.