THERE HAS ALWAYS been one major weakness in the 1968 Fair Housing Act. Its provisions, barring discrimination on the basis of race, color, religion, national origin or sex, are difficult to enforce. The House of Representatives gets a chance to remedy that this week.

Under the original act, a victim of discrimination can complain to the Department of Housing and Urban Development. It can then attempt to settle the dispute by conciliation. If that fails, there is nothing more the government can do. The victim can go to court, but the government can file suit only if there has been a "pattern" of discrimination.

Under the proposal that has emerged from the Judiciary Committee after nine years of prodding, HUD could use administrative actions to enforce the law. Individual complaints could be heard by administrative law judges who would have power to order an end to discrimination and to levy fines up to $10,000. Decisions of these judges could be appealed to federal court.

This is a straightforward method of putting teeth into the Fair Housing Act. It would provide a much cheaper and more efficient way to resolve complaints without burdening the courts. Some complaints might even be decided before a house was sold or an apartment rented.

But a peculiar fight is under way on Capitol Hill. Two congressional opponents, Reps. Ronald M. Motti and John W. Wydler, recently wrote to more than 4,000 mayors and county officials, telling them that this proposal would let administrative judges regulate local zoning. The National Association of Realtors has been telling congressmen that HUD would exercise so much control over the administrative judges that procedural safeguards would be wiped out.

There is no logical basis to this opposition. Other changes in the law would make it harder -- not easier -- for the federal government to intervene in local zoning matters. And administrative law judges are already involved in other departments in proceedings much like those contemplated in this proposal. An attack based on the idea that they could not be impartial in civil rights cases at HUD is the equivalent of an attack on the whole system of administrative law.

Realtors, along with real estate appraisers and the insurance industry, don't oppose the principles of non-discrimination proclaimed by the Fair Housing Act. They just don't want them enforced efficiently.