The Rev. Jerry Falwell, head of the Moral Majority, yesterday accused Democratic presidential nominee Walter F. Mondale of "hypocrisy" for trying to use his religious background for political advantage even though he said he would not do so.

"Nobody has ever questioned Mr. Mondale's faith . . . . I do question his motives," Falwell said yesterday on "Face the Nation" (CBS, WDVM). "When he comes off saying 'my father is a minister, my wife's father is a minister' . . . and then in the next paragraph says 'I've never used religious influence to promote myself' -- that, to me, is hypocrisy."

Falwell was referring to the speech Mondale gave last week to the B'nai B'rith, a Jewish service organization, in which he noted that for the first time in his public life, he felt the need to "defend" his religious faith in a political campaign.

Falwell also said that Mondale, "who doesn't have a prayer, even a voluntary prayer, of being elected, is creating a non-issue" by suggesting that President Reagan is trying to blur the line separating church and state.

"The whole thing is a straw man," he said on "This Week With David Brinkley" (ABC, WJLA), where he also appeared. "Mr. Mondale looks at an invulnerable president with a 20-point lead and decides . . . 'we must create an issue here.' It's a farce. No one is questioning anyone's religion. No one wants to establish a Christian state . . . . We want a nation under God. That's all this president, and every president since Washington, has called for."

Falwell took issue with the charge by Mondale and others that the fundamentalist Christian political movement Falwell leads tries to suggest that people who disagree with them are ungodly.

"I don't think for a moment that anybody, just because they are defending the rights of the unborn and standing up for traditional values. . . is telling people that you are against God if you don't vote this way," he said.

He also claimed that his benediction at the Republican National Convention in Dallas last month, in which he called Reagan and Vice President Bush "God's instruments for rebuilding America," had been misinterpreted by Mondale.

"In Romans 13, Paul said that the powers that be are ordained of God. That would mean that the leaders of the Soviet Union, and every nation on earth, whether they know it or not and are willing to admit it or not, are God's instruments for the purpose of peace and building our society."

Asked if he believed that Democratic leaders, too, were "God's instruments," he said, "Of course. . . absolutely."

Mondale declined through a spokesman to respond to Falwell's comments yesterday.

On the Brinkley show, not all the attacks were aimed at Mondale. Sen. Daniel Patrick Moynihan (D-N.Y.) chided Reagan for trying to "stigmatize as anti-religionist" those who disagree with him about school prayer and abortion.

Moynihan added, "I absolutely believe President Reagan when he says he does not want to establish a state religion -- that would require him to attend services."