The AFL-CIO, angry about President Carter's new budget cuts, warned again yesterday that it may bolt the "national accord" that it signed with the White House last fall and abandon the administration's voluntary wage-price program.

In a speech before a newspaper editor's group, Lane Kirkland, the federation's president, said he doesn't know "how long we will continue to participate" in the administration's tripartite Pay Advisory Board.

Although Kirkland stopped short of announcing an actual break with the administration, federation sources said the subject could come up at the next AFL-CIO executive council meeting May 6.

The move marked the second time a top AFL-CIO official has raised the possibility of a split since the federation soured on Carter's new austerity program early last month. Yesterday's speech clearly was intended to send Carter a message.

The development came as, separately, top White House economist Charles L. Schultze told an audience the current 18 percent inflation rate could drop sharply in the next three months if mortgage rates ease and oil prices slow slightly.

Although decling to make any firm predictions, Schultze outlined a case in which a moderate drop in home mortgage rates would pare the overall inflation rate quickly to as low as 8 percent.

Schultze also lambasted as "dead wrong" the proposals being advocated by GOP presidential frontrunner Ronald Reagan and other Republicans which call for sharp across-the-board government spending.

He said Carter also is willing to propose sizable tax cuts to spur productivity and investment. But, he added, "Our first step is to cut spending." He said tax cuts won't eliminate "the need for demand restraint."

Meanwhile, Capitol Hill sources disclosed that new estimates by the Congressional Budget Office show Carter's new March 14 budget proposals will produce a surplus of only $6 billion instead of the $16.5 billion he is projecting.

The differences stem from the CBO's higher estimates of how much defense spending Carter's budget actually would require increases in projected interest costs and a more pessimistic assumption about cost-saving measures.

The CBO calculations show that, not counting Carter's $11 billion oil-import fee, the budget would be in deficit by $4 billion in fiscal 1981 rather than-yeilding a $4.5 billion surplus as the White House has portrayed it.

However, sources said the CBO figures are unlikely to affect congressional action on the budget. Both the House and Senate budget committees have used higher estimates than the administration in computing their own budget figures.

The administration's revised budget, unveiled by Carter less than a week ago, calls for $611.5 billion in spending and $628 billion in expected revenues, including the import-free monies, for a surplus of $16.5 billion.

By comparison, the CBO's new calculations show probable outlays at $621.5 billion, with revenues at $627 billlion and a surplus of $6 billion. The agency, which is non-partisan, is the budget-analysis arm of Congress.

The admonishment by Kirkland was by far the most strongly worded warning the federation has issued about the possibility of a break. The "national accord" was negotiated last fall in a major election-year coup for the administration.

AFL-CIO leaders have been visibly upset over Carter's new budget-cutting proposals, which concentrate on programs that would affect cities and the poor.

But federation sources said it was doubtful the AFL-CIO actually would vote to break with the administration despite its anger over Carter's budget cuts.

Meanwhile, the Commerce Department said sales of new, single-family homes fell 9.5 percent in February to the lowest level since the 1974-75 recession.

Sales occurred at a seasonally adjusted annual rate of 532,000 units in February, down from January's 588,00 units and 26 percent below the 715,000 units of February 1979.

That made February sales the poorest since March 1975, when high interest rates and a shortage of mortgage money pushed sales down to an annual 477,000.