WASHINGTON (AP) _ Distict of Columbia voters will decide Tuesday whether to stiffen existing rent control regulations by eliminating recently enacted provisions that would decontrol many of the city's apartments.

The referendum has been sharply debated because it seeks to return protection against landlords that was taken away by city council last spring.

Most residents of Washington are tenants, and supporters of the measure say it has a good chance of passage.

''Anytime you reduce the amount of units under control you reduce the amount of affordable housing in the city,'' said Steve Rollins of the Emergency Committee to Save Rental Housing. ''If you phase out rent control, people will be forced to move.''

But landlords who oppose rent control say a referendum is not a proper forum for the issue, and Mayor Marion Barry Jr. agrees.

''As a general statement, which has nothing to do with the issues involved here, I think a referendum is not a good way to run a government,'' said Donald Slatton, executive vice president of the Apartment and Office Building Association of Metropolitan Washington.

Barry said there are enough protections for tenants in the law.

''I don't believe you should run government by referendum. There was enough in the bill for me to sign it,'' Barry said.

In addition, civil rights groups oppose the referendum because it would remove certain tax incentives landlords currently have to renovate run-down properties.

About 200 communities in the nation have some form of rent control, according to Jean Hussey, of the National Multi-Housing Council in Washington. Most are in New York, New Jersey and California.

Washington has had rent control for 14 years. It applies to about 65 percent of the city's 159,000 occupied rental units.

About 60 percent of the 252,000 residences in the city were rentals, according to 1981 Department of Housing and Urban Development statistics, the most recent figures available.

Even if the referendum succeeds, landlords can raise rent once a year based on the consumer price index, with a cap of 12 percent.

But the referendum would void four provisions of a law the city council narrowly passed in April.

One provision would lift controls in 1989 on all rental apartments once they become vacant, provided the city's vacancy rate is at least 6 percent and a tenant assistance program is in place.

Another section exempts from rent control single-family homes owned by fewer than five individuals, rather than corporations, once they become vacant.

A third provision would at the owners' request and on a case-by-case basis, lift controls on buildings that were at least 80 percent vacant as of April 30.

The fourth section being challenged provides for decontrol of buildings declared to be ''distressed'' properties that could receive tax breaks and other assistance as incentives for landlords to restore them.

That last provision prompted civil rights group including the National Association for the Advancement of Colored People, the Southern Christian Leadership Conference, and Operation PUSH, to come out against the referendum at a news conference Wednesday.

Though district residents have voted on several initiatives that seek to create law, a referendum, which would overturn established law, has never been presented in the 10 years Washington has had home rule.