The Reagan administration angered some women's groups yesterday by proposing new affirmative action regulations for federal contractors that would limit awards of back pay to workers found to be victims of discrimination.

In addition, the rules would allow contractors to meet obligations to hire women and minorities even if those workers are concentrated in entry-level, low-paying jobs.

The proposals, published in yesterday's Federal Register, also would exempt contractors from affirmative action requirements at job sites where federal contracts are not involved.

Karen Nussbaum, executive director of Nine to Five, a national organization of women office workers, and president of District 925 of the Service Employes International Union, said in a written statement:

"The Reagan administration is clearly not concerned with the rights of women and minorities but with the privilege of corporations. The 44.5 million women who work can no longer afford to sit back and watch as this administration and Congress strip away our rights one by one."

Judith Lichtman, executive director of the Women's Legal Defense Fund, charged that the changes would create a low-paid "helper" category for women in the construction industry.

"This is the opposite of equal pay, the opposite of affirmative action," she said.

There had been some concern among women's groups that the Labor Department's Office of Federal Contract Compliance Programs would totally eliminate back pay as a remedy for workplace discrimination. The new proposals by would not go that far, but would:

* Limit back pay to "identifiable victims of discrimination" who had suffered economic loss.

* Limit the contractor's liability to the "number of jobs, job opportunities and wage or career opportunities which would have been available," if there had been no discrimination.

* Set a maximum of two years of back pay to victims of discrimination. That amount would be reduced by any interim earnings a worker received while the case was considered. The U.S. Chamber of Commerce has urged that the right to back pay be eliminated entirely.

In the construction field, OFCCP wants to retain the present hiring goal of 6.9 percent for women. But it would apply that to the entire on-site workforce, rather than to each separate craft or job category as is now done.

It specifies that the employer will be considered to have made a "good-faith effort to achieve the goal" if at least 6.9 percent of the hours worked in entry level positions--"helpers, trainees and apprentices"--were worked by women.

Marcia Greenberger of the National Women's Law Center warned that this would lead to a policy of keeping women in low-level jobs as helpers rather than in the higher-paying categories such as plumbers and electricians.

"The construction industry has historically been an exclusive preserve for men. This administration is making a mockery of the principle underlying the current requirements--that women should work in all the trades, at all levels--just like men," she said.

The Labor Department has set a 30-day period for public comment on the proposed regulations.