The Carter administration yesterday urged Congress to cut $5 billion from next year's budget, but refused to say where the spending cuts should be made.

Budget director James T. McIntyre Jr. told the Senate Budget Committee that Congress, in setting its final spending target for fiscal 1979 (which starts Oct. 1), should cut $5 billion from the $496.6 billion President Carter earlier proposed to spend.

White House press secretary Jody Powell, in an unusual action, called reporters' attention to McIntyre's testimony and said Carter endorsed the call for a $5 billion spending cut next year.

But neither McIntyre, when pressed by senators, nor Powell, when asked by reporters, came up with specific programs to cut to trim spending by $5 billion.

McIntyre said, "I believe that by a combination of tighter estimates, eliminating the discretionary spending increases over the president's budget implicit in the first [tentative 1979 congressional budget] resolution and perhaps even an across-the-board cut, we could achieve a substantial reduction in 1979 spending."

He said more restraint is needed in next year's budget because unemployment "has declined more than had been expected and . . . prices are rising rapidly."

Powell told reporters at the White House that it "is necessary to exercise restraint in fiscal 1979 if we're going to reduce the deficit in 1980."

McIntyre, before the Senate committee, rejected any cuts in administration-proposed programs such as public service jobs or its new public works construction programs.

McIntyre said he wanted to wait and see if the dramatic decline in unemployment to 5.7 percent in June would stick before the administration would consider taking another look at its job programs.

Pressed by Chairman Edmund S. Muskie (D-Maine) and Sen. Lawton Chiles (D-Fla.) to come up with specific programs that could be cut back, he said he would try to make up a list.

One angry Senate source said that McIntyre was telling the committee, in effect, to keep all the new programs that Carter wants, such as his urban program, but to cut any programs that Congress wants but the president does not.

"He can't draw up a list of any programs to cut. The Cabinet won't stand for it," the Senate official said.

Labor Secretary Ray Marshall, as if to prove that point, said later in Michigan that the administration has no plans to reduce any of its jobs programs despite the improvement in unemployment.

"There are those who are now saying that unemployment has declined so much that we no longer need a large-scale public service jobs program." Marshall said in a speech prepared for delivery to the Michigan AFL-CIO. "This is a very dangerous misconception . . ."

The tentative budget Congress adopted last spring estimated the federal government would spend $498.3 billion in fiscal 1979. That is lower than the president's original January estimate of $500 billion, but higher than the revised administration estimate of $496.6 billion, released July 6.

Congressional sources said, however, that when the Congressional Budget Office today submits its reestimate of 1979 spending, it will be several billion dollars less than $496.6 billion.

Although the president proposes a budget each January, Congress, through its budget process, makes the final decisions about how much the federal government will spend in each area.