Defense Secretary Caspar W. Weinberger yesterday referred to the stakes in El Salvador's civil war in terms of global competition between the United States and Soviet Union, saying a communist victory in El Salvador could pressure the United States to pull out of Europe and Asia to defend its southern borders.

Weinberger, interviewed on "Face the Nation" (CBS, WDVM), also said that "there is no question" that with additional U.S. military aid, the Salvadoran army "can prevail" over the Marxist guerrillas.

If that happens, "we'll all be a lot safer than having another communist foothold such as Cuba right on the mainland," he added.

The defense secretary's comments came on the heels of President Reagan's request to Congress last week for an additional $110 million in military aid for El Salvador on the grounds that the conflict threatens U.S. national security.

Speaking yesterday on "Meet the Press" (NBC, WRC), Colorado Sen. Gary Hart, an announced candidate for the 1984 Democratic presidential nomination, said he would oppose further aid to El Salvador unless strict conditions are attached to it because it is not possible to "achieve democracy out of the barrel of guns."

Reagan's view that the Salvadoran conflict threatens the United States was endorsed by Senate Armed Services Committee Chairman John G. Tower (R-Tex.). On "This Week with David Brinkley" (ABC, WJLA), Tower said, "I think the domino theory could very well work in Central America. After all, it worked in Indochina."

Weinberger suggested several times yesterday that the Salvadoran civil war poses a threat to the United States' southern borders. "The simple fact is the El Salvadorans have chosen a government, and it is certainly very much against our interests to allow that freely choosen government to be subverted and turned into another very repressive regime that would be then much more in a position to make that kind of communist gain further north up toward Mexico and toward our own borders," he said.

"Their purpose is, as we see it," he said, "to attack the United States in . . . this incremental way, from the south, knowing that as they got closer that would mean that we would have to--or would at least have strong pressures formed--to pull ourselves out of Europe, and out of Japan and Korea, and establish some sort of a Fortress America concept, which would serve the Soviet purposes very well globally."

Even as he cast the threat in such terms, however, Weinberger ruled out more direct U.S. participation in the Salvadoran conflict. "What is essential is to solve this matter at the lowest possible level of participation and conflict by the United States," he said.

He said it is "vital" that Salvadoran troops be resupplied by the United States to match supplies received by guerrilla forces "every night" from Nicaragua, Cuba and the Soviet Union.

Weinberger said U.S. military aid to El Salvador will end when "the democratic effort that is going on in El Salvador is allowed to continue unimpeded and unhampered by adverse, communist-sponsored military activity. Now, I can't give you the hour or the day that's going to happen . . . . " But, he said, the administration "is trying to bring that day closer."