President Reagan said yesterday that "born-again budget balancers" on Capitol Hill are "suffering from a crisis of faith" in the drive to reduce federal deficits, and called on Congress to approve a wide array of domestic budget cuts by Easter.

"If there isn't enough courage to approve these cuts, then at least give me the authority to veto line items in the federal budget," Reagan said in his regular Saturday radio broadcast. "I'll take the political responsibility. I'll make the cuts and I'll take the heat."

In the Democratic response, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) accused the administration of "trying to obstruct our efforts to help the American farmer," and said a strong agricultural economy is "a matter of basic national security."

The jousting came as the House and Senate last week passed farm-relief bills that Reagan has threatened to veto, and White House officials became increasingly concerned about lagging efforts by Senate Republicans to reach agreement on a deficit-reduction package. The officials said Reagan's speech was designed to breathe new life into the budget-cutting drive.

Some Republicans have complained privately that Reagan's rigid stance on defense spending and Social Security cost-of-living adjustments has stalled their efforts to get GOP agreement on domestic cuts.

Reagan yesterday directed his scorn at Democrats and interest groups. He mocked the House Budget Committee hearings held around the country in February as a "political spectacle" in which members were "inviting special-interest groups to resist every proposal for budget savings."

The president, who had previously skirted the politically sensitive cuts in his fiscal 1986 budget, yesterday fired back at those who have attacked his budget reductions in federal aid for mass transit, including Washington's Metro system, college student loans, Amtrak, urban aid, and subsidies for farmers and big and small business.

The budget that Reagan sent to Congress last month included a $180 billion deficit, sharp domestic-spending cuts, a continued defense buildup and no major tax increases.

The president said his budget followed the "spirit" of the Grace Commission recommendations to "cut spending growth without harming the needy or impairing any essential purpose of government." Instead, Reagan said, he is seeking to cut spending "where it's wasteful, where it's not urgent, and where it subsidizes some people at everyone else's expense."

"Why should any taxpayers subsidize the operating costs of the Washington, D.C., transit system, an area with the second-highest per-capita income in America?" Reagan asked. His budget proposes an end to mass transit operating subsidies; Metro officials have said this would cost the system $18.5 million a year.

Reagan said his proposed cuts "have been greeted by a chorus of boos from -- guess who? -- the very people who told us again and again that tough action on deficits couldn't wait. Today, they say, now is not the time."

The president said earlier this year that he was "actually becoming hopeful that new courage was taking root" to cut the deficit, but "that was a hasty judgment" because "just one month ago, the mood of the born-again budget balancers abruptly changed. Now they're suffering from a crisis of faith."

"I won't deny all the groups I mentioned represent valid interests which may seem compelling. But there is a larger interest to represent, more compelling than all the rest -- the freedom and security of American taxpayers . . . ," he said.

"Well, as long as I'm president, we're not going back to the days when America was fast becoming an impotent democracy too weak to meet defense commitments or to resist communist takeovers and, yes, too weak to stop a federal spending machine from impoverishing families and destroying our economy with runaway taxes and inflation."