The Reagan administration is proposing a new civil rights bill aimed at strengthening enforcement of the 1968 Fair Housing Act, Secretary of Housing and Urban Development Samuel R. Pierce Jr. announced yesterday.

"Tough enforcement and swift justice are at the heart of the bill," Pierce said at a luncheon at the National Press Club.

The legislation would help the administration fight charges that it has turned its back on blacks and other minority groups.

But civil rights groups yesterday said the administration bill would not go far enough. They said they prefer an alternative introduced two weeks ago by Sens. Charles McC. Mathias Jr. (R-Md.), Edward M. Kennedy (D-Mass.) and 37 other senators that would create the equivalent of special fair housing judges inside HUD.

The Fair Housing Act forbids discrimination in sale or rental of housing because of race, color, religion, sex or national origin.

But it relies principally upon conciliatory procedures to resolve complaints. "It has become clear that the Fair Housing Act falls short of its promise because of a gap in its enforcement mechanism," Pierce told a news briefing later.

As described yesterday, the proposal would authorize the HUD secretary for the first time to send allegations of discrimination against a single individual to the Justice Department with recommendations that lawsuits be filed when complaints cannot be resolved within a 30-day conciliation period.

"This keeps the burden of enforcement where it belongs, on the federal government rather than on the individual victim," Pierce said. Currently, the Justice Department can sue only in cases involving a pattern or practice of systematic discrimination, not in individual cases.

The bill would also create substantial civil penalties that could be sought from landlords who violate fair housing laws: up to $50,000 for a first offense and up to $100,000 for a second offense. Antonio Monroig, HUD assistant secretary for fair housing, said the potential penalties would act as a deterrent to discrimination and strengthen the process of conciliation.

Civil rights groups yesterday did not embrace the administration proposal, saying it did not go far enough. Ralph Neas, executive director of the Leadership Conference on Civil Rights, a coalition of 165 national organizations, called the effort to make improvements "a positive change from the Reagan administration's systematic attacks on our civil rights," but called the specific proposal "clearly inadequate."

"The administration proposal is a judicial remedy," Neas said. "What the civil rights community wants is an administrative remedy with judicial review."

The administrative remedy is included in the measure introduced two weeks ago in the Senate. It would establish an administrative procedure in HUD with hearing examiners assigned to handle complaints. Pierce said that the administrative mechanism in the Mathias-Kennedy bill would "delay action in a lengthy, bureaucratic process."

Kennedy yesterday called the administration's proposal "a half-hearted approach" that was "plainly inadequate . . . . Women, blacks and Hispanics denied a home for their families need speedy relief, not long lawsuits."

The proposal was approved by President Reagan in a meeting with Pierce and Attorney General William French Smith yesterday morning.