Civil rights groups and business interests directed criticism yesterday at the Reagan administration's move to weaken federal job discrimination rules for firms doing business with the government, but for opposite reasons.

The administration proposal drew heavy fire from the civil rights organizations, who said it would set back the cause of equal employment opportunity, but the U.S. Chamber of Commerce complained that the proposal did not go far enough.

Eleanor Smeal, head of the National Organization for Women, predicted that a backlash of opposition to Reagan's affirmative action policies will boost the Equal Rights Amendment drive, now in its do-or-die final stage with 10 months in which to win ratification by three more states.

"Equal opportunity will become more a slogan than a law" under the newly revised rules, Smeal said in a comment typical of a number of groups. Noting that today would be the 61st anniversary of the date women won the right to vote, she added that Reagan's efforts to move backward reinforce the need for the constitutional amendment.

The Black Leadership Forum said, "These proposals give further evidence that this administration is turning its back on the needs of black people for work and dignity in a period of unprecedented unemployment, which gives rise to spiritual agony and social frustration."

Joyce Miller, head of the Coalition of Labor Union Women and the only woman on the AFL-CIO executive council, called the plan "a disaster, a clear message to the enemies of equal opportunity for women and minorities that they can feel free to evade and avoid the law . . . . "

The new plan, published yesterday in the Federal Register, would exempt almost three-fourths of the 200,000 firms with government contracts from preparing written affirmative action programs, according to Labor Secretary Raymond J. Donovan. But he said it would still cover nearly 77 percent of the workers protected under the old rules. Among other things, the proposal reduces various paperwork requirements, especially for smaller firms, eliminates the review of a firm's hiring record before a contract is awarded and reduces the affirmative action requirements for construction contractors.

Lonis C. Ballard, president of Blacks in Government, said the proposal "sends out a signal . . . that there will be an easing up with regard to the gains we have made in the last two decades."

The U.S. Chamber of Commerce opposed the changes on the grounds that they did not ease up enough. The chamber urged a substantial revision of the 1965 original executive order on which the federal affirmative action program is based.

"The Department of Labor missed an excellent opportunity to achieve true reform and to place its mark on the second generation of affirmative action programs," chamber labor law attorney John B. Brandenburg said in a statement. "Our concept of affirmative action embodies the belief that the road to equal employment opportunity should not be paved with new varieties of discrimination against other groups."

The federal process provides for a 60-day comment period beginning with yesterday's publication. The plan would take effect after 90 days. One agency with approval rights, the Equal Employment Opportunity Commission, has refused to endorse the plan, and the disagreement might have to be resolved by the White House.