Mixed signals from the Reagan administration point to an uncertain future for fair housing under the Department of Housing and Urban Development.

HUD is charged with administering the nation's fair housing law, Title VIII of the 1968 Civil Rights Act, which prohibits discrimination based on race, sex, national orgin or religion, in a wide range of activities related to the sale and rental of housing.

In the past, the department has chosen not to flex all the fair-housing muscles it has. Now the Republicans, though decisive about budget cuts, cannot seem to decide whether to boost the cut back HUD's fair-housing commitment.

Attention to upgrading HUD's powers to police both public and private housing availability tend to focus on legislative proposals to hand the department a bigger stick. Recently, bills similar to measures defeated last year have been introduced that would allow HUD to enforce antidiscrimination as well as investigate and conciliate complaints.

In his nomination hearings, HUD Secretary Samuel R. Pierce Jr. supported strengthening the fair-housing law. But the administration has yet to indicate its support of either of the measures pending in the House and Senate. Pierce told reporters recently that the administration is preparing its own legislative proposal, a proposition many civil rights advocates say would put few teeth into HUD's bite and might even weaken the law on the books.

Meanwhile, Pierce has withdrawn regulations issued under the Carter administration designed to interpret and clarify the 1968 law.

Before he left HUD, Sterling Tucker, former assistant secretary for fair housing and equal opportunity, called HUD's failure to write these regulations a "disgrace." He promised that the Title VIII rules would emerge from HUD before he left.

The result was 163 pages defining what HUD considered discriminatory practices by landlords, lenders, real estate brokers, property insurers and appraisers. The rules detailed the types of complaints HUD would accept for investigation and what standards the department would use to determine whether discrimination had occurred.

But they'd been held in HUD too long, in part due to a political decision not to rock the boat until after Congress approved the Fair Housing Amendments Act of 1980.

The plans backfired. Carter lost in November, and conservative senators, testing their new mettle, killed the amendments with a filibuster in early December. The rules, sent to Congress for review in January, were pulled back into the department by the new administration in a general freeze on all pending regulations.

They wee tagged for special consideration after conservative Sens. Jake Garn and Orrin Hatch, both Utah Republicans, and Strom Thurmond (R-S.C.) wrote Pierce charging that the rules were attempting to accomplish what the Senate, through defeat of the amendments, had indicated it would not tolerate.

The rules will not be reissued in their present form, Pierce recently announced. In fact, the department may wait on revising them until a new fair-housing amendments act is passed, he said.

Another fair-housing regulation, also caught in the Republican regulatory freeze, would have detailed HUD's duties for carrying out a last-minute executive order by then-president Carter. The order emphasized HUD's responsibility to see that all federal housing and urban development programs are administered "in a manner affirmatively to further fair housing." Without the accompanying regulation, the order will have little effect.

The new administration also has not yet filled the post Tucker left in January. Though no name for the position has been sent to the Senate for approval, a top contender is said to be Antonio Monroig, a lawyer who head Puerto Rico's Municipal Services Administration.

Monrig comes highly recommended by Sen. Howard Baker (R-Tenn.), for whom he campaigned in the Puerto Rican presidential primary. His experience with municipal governments and his concern for Puerto Ricans are his major qualifications for the job, according to Baker's staff.

On the positive side, the funding for Hud's two fair-housing programs, totaling $5.7 million, was not marked for cuts in the Reagan administration budget. Pierce reportedly went to bat to save $2 million the Office of Management and Budget had intended to slice.

Part of those funds, $3.7 million, will be used to build the capacity of state fair-housing agencies to process discrimination complaints. Title VIII requires HUD to refer complaints to agencies that operate under laws "substantially equivalent" to federal statute. But until the Fair Housing Assistance Program was started last year, HUD offered only technical assistance, without money, to help state processing.

Hud has approved some 27 states for referrals. In large chunks of the South and West, where states have either unacceptable or no laws at all, the department's regional offices still must handle all complaints.

The remaining $2 million in fair-housing funds will support the citizen groups that monitor and evaluate voluntary marketing agreements between HUD and various housing industry groups.

The only hitch to those plans is that the agreement with the National Association of Realtors, the largest group participating in the voluntary compliance program, expires this month. The Realtors have not yet announced whether they'll continue the agreement.

Pierce also has decided to continue funding nine private fair-housing groups around the country that identify and processs bias complaints and refer them to HUD field offices.

The groups use testers who pose as renters and buyers to determine if racial discrimination is occuring in the sale or lease of housing.

Although urged by the U.S. Commission on Civil Rights to use testers itself, HUD has shied from the practice, preferring instead to use results gathered by other organizations.