The Carter administration has hit something of a snag in its efforts to work out a compromise on the controversial Humphrey-Hawkins full-employment bill, now being pushed as a major policy goal by the Congressional Black Caucus.

Although negotiators for the White House and for the bill's sponsors have narrowed some earlier disputes in key areas, they remain at loggerheads over two fundamental questions that have held up agreement for months - what constitutes "full" employment and how fast to reach it.

The administration has agreed to accept an "interim" goal of reducing the unemployment rate, now 6.9 per cent of the work force, to 4 per cent by 1981 - a target that President Carter already has embraced anyway in other election campaign promises.

The barrier remaining is what to do after that. Sponsors of the Humphrey-Hawkins bill want Carter to adopt a goal of 4 per cent or lower for 1982 and beyond. But the administration wants to avoid any specific numerical target, contending it would be unrealistic and tie policymakers hands.

The stalemate has become crucial because of increasing pressures on the President to come out in support of the Humphrey-Hawkins measure which he pledged to back during the campaign but later sidestepped on advice of aides.

At a Sept, 24 dinner, the Presidnt promised Black Caucus members "a final decision" on the form of the bill within a week or 10 days. And last week he pledged to announce his support "within the next few days."

Yesterday, however, Jody Powell, the White House press secretary, cautioned that "I don't think it is correct to say that agreement has been reached" on the bil, and hinted that "no final decisions" were likely for another week or two.

That means Carter is unlikely to have anything new to say about the measure when he visits inner-city neighborhoods in Detroit on Friday for a highly touted "town meeting" with black leaders.

The President has come under increasing criticism from black organizations in recent months for not endorsing the Humphrey-Hawkins bill and other liberal-backed social legislation.

Negotiations on the Humphrey-Hawkins measure so far have been conducted essentially at the staff level. The proceddings have been reviewed by Charles L. Schultze, the President's chief economist, and top White House aides.

The congressional negotiators made a serial of final counter-droposals last week, and the White House promised to let them know today or tomorrow whether the administration would agree to them.

Carter is expected to meet with congressional proponents and Black Caucus members next week, no matter how the talks turn out. The measure is sponsored by Sen. Hubert H. Humphrey (D-Minn.) and Rep. Augustus F. Hawkins (D-Calif.).

Talks over the past several months have resulted in some concessions by both sides, primarily on secondary issues, but according to insiders these have failed to resolve many of the basic differences between Carter and the liberals.

The campaign version of the bill, unveiled early in 1976, would have set a formal target of reducing unemployment to 3.8 per cent within four years, and then committed the adminstration to a $28 billion program to achieve it.

It also would have set elaborate job-creating machinery designed to guarantee every citizen the "right" to a job, no matter what the cost, with the government serving as "employer of last resort" when the job market is tight.

The version hammered out so far by negotiators would soften the employment goals, reduce the job-creation requirements to mere authorization to propose new job programs, not a formal mandate, and make the phrase "right to a job" symbolic.

However, negotiators still are at odds, both over the umemployment taget for the longer run and how far to require the President to go in creating new jobs during periods of high inflation.

The administration already is falling behind in meeting its own economic targets. The jobless rate has lingered longer than expected at about the 7 per cent level, and inflation has remained unchanged, rather than slowing down.