The controversial Humphrey-Hawkins "full-employment" bill hit a possibly fatal snag yesterday when the Senate Budget Committee demanded major changes in the measure that could prevent passage before Congress adjourns.

In a surprise move, the panel voted to clear the bill for floor action only if sponsors agree to drop a series of provisions that would allow the Joint Economic Committee to alter the annual congressional budget resolution.

The action came despite a pledge by President Carter last Saturday that the White House would push actively to revive the dying measure. The bill would commit the government to reducing the jobless rate to 4 percent by 1961.

Meanwhile, leaders of the Congressional Black Caucus, who pressured Carter into renewing his support for the bill last weekend, complained publicly yesterday that the White House had not done enough to press for Senate floor action.

Rep. John Conyers Jr. (D-Mich.), who embarrassed Carter last week by stalking out of a White House meeting on the measure, told reporters there were "blatant and obvious contradictions" between the president's promise and performance.

"If their commitments mean anything," Conyers said, "this bill will be calendared and a date set to begin debate." So far, he asserted, "we are precisely no closer . . . than we were a week ago."

Immediately after the Budget Committee vote, sponsors of the measure made plans to obtain agreement from the leadership on a specific time for a floor vote on the bill. However, most observers were doubtful they would get it.

Opponents have threatened to filibuster the measure to death if it comes up on the floor. Yesterday, budget panel Republicans moved to delay any floor vote on the committee's proposal until Wednesday - dimming prospects for any action.

The objections posed by the Budget Committee amount essentially to a fight over turf between that relatively conservative panel and the more liberal Joint Economic Committee, which is supporting the Humphrey-Hawkins bill.

If the provisions the budget panel protested were enacted, the JEC would be empowered to propose its own substitute tax and spending targets for the ceilings recommended by the Budget Committee each year.

Sen. Edmund S. Muskie (D-Maine), Budget Committee chairman, complained the provisions effectively would establish a "rival" congressional budget process to compete with the one the Budget Committee oversees.

However, sponsors of the measure say deletion of the key provisions "would gut the bill of the only real teeth" for ensuring that Congress pursues the economic goals set by the legislation.

The proposal demanding that sponsors of the bill drop the key provisions passed on a vote of 9 to 2, with only Sen. Alan Cranston (D-Calif.) and Wendell Anderson (D-Minn.) opposing it.

The Budget Committee won the right to act on the bill because the measure would authorize appropriations to finance government studies on economic issues. Without a formal waiver, the bill could be ruled out of order.

The measure is named for its two original sponsors, the late Sen. Hubert H. Humphrey (D-Minn.) Rep. Augustus F. Hawkins (D-Calif.). The bill already has passed the House and won approval from two Senate committees.