AFL-CIO President Land Kirkland delivered a scathing attack on President Reagan's economic program on Capitol Hill yesterday as congressional Democrats continued to send contradictory signals about their response to Reagan's initiatives.

"The Reagan budget constitutes the most costly roll of the dice ever proposed for this nation by economic policy makers," Kirkland told the House Budget Committee in the harshest criticism that the administration's spending and tax reduction plans have drawn so far in congressional testimony by a major public figure.

"The administration is gambling with the well-being of those who can ill afford to gamble, in order to provide a sure winner for the wealthy who are not asked to take any of the risk," Kirkland said.

Responding that he was "troubled" by the tenor of Kirkland's testimony, Budget Committee Chairman James R. Jones (D-Okla.) said it was "180 degrees different from what is being recommended to this committee" and contrary to what he called a "mandate" to cut government spending.

But, even as Jones was speaking, Democrats on the Senate Labor and Human Resources Committee, led by Edward M. Kennedy (Mass.), held a forum to dramatize what Kennedy called the "impact in human terms" of the president's more than $40 billion in proposed budget cuts. When Kirkland appeared with United Auto Workers President Douglas A. Fraser before the Senate Democratic panel, there was no dissension -- only mutual predictions of dire results.

Meanwhile, House Democrats mounted what was advertised in advance as the opening shot of a Democratic response to the Reagan economic program, a "testing of the waters" to see how far the party should go in criticizing Reagan economic policies. But only half the designed speakers turned up for what amounted to desultory complaints about interest rates.

Asked in advance of the effort whether it meant that the "honeymoon" between Reagan and House Democrats was over, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) responded, "We're not ready to play hardball yet. . . . We're not obstructing. We're going along. We're giving them plenty of room."

Kirkland, however, clearly did not advocate a give-'em-enough-rope approach as he called for virtually total rejection of Reagan's program as "inequitable, unfair and shortsighted." Asked at one point whether Congress should give Reagan what he wants on the theory that this is the only way to prove his plan won't work, Kirkland said it would amount to "giving hypocrisy a bad name."

Kirkland, a prime mover in a coalition of 157 groups fighting Reagan's economic program, challenged the basic premise of Reagan's budget-_cutting drive: that spending and deficits cause inflation. In fact, he said, spending retrenchment and inflation have gone hand-in-hand in recent years.

Kirkland was especially critical of the administration's plan to cut trade adjustment assistance for workers whose jobs are jeopardized by imports, restrict money available for Medicaid, eliminate the minimum Social Security benefit and cut out public service jobs. "The cuts do not cut the cost of social programs," he said. "They defer some and shift others to the budgets of the states, localities and the poor."

As for Reagan's proposed tax cut of 30 percent over three years, he said: "Those families who have suffered the sharpest declines in living standards due to inflation get the least benefit from the tax cut proposal." The administration's business tax cuts, he added, would help "finance speculative ventures, corporate takeovers, industrial flight or foreign expansion at the expense of U.S. jobs."

If Congress wants to cut costs, Kirkland said, it should consider ending deferral of taxes on overseas profits, the oil depletion allowance, foreign tax credits and investment tax credits. Kirkland also advocated a tax credit to help offset Social Security tax increases and a targeted business tax cut to help what he called the "truly deserving needy" of the business world.

In addition to the criticism from Democrat Jones, Kirkland drew some heavy fire from Republicans on the Budget Committee.

Rep. Delbert Latta (Ohio), its ranking minority member, noted polls showing that 50 percent of union members voted for Reagan and questioned whether "you speak for the rank-and-file members of your unions." One could even "come to the conclusion that you do not believe in the free enterprise system, which has given your members the highest standard of living of any industrialized nation on earth and which, incidentally, has made your job possible," added Latta.