KNOXVILLE, Tenn. (AP) _ Faced with a $25 billion debt, the Tennessee Valley Authority will probably scrap plans to complete three unfinished nuclear reactors, its chairman said.

Chairman Craven Crowell said it is ''highly unlikely'' the three reactors will be completed as nuclear-driven electrical plants. He has said a conversion to natural gas is possible.

Crowell was to make an announcement Monday and also outline plans on how TVA, one of the nation's largest power producers, will curb its heavy borrowing.

TVA's debt is tied to the failure of its once-grand vision for a 17-reactor power system.

Eight of the 17 planned reactors have already been scrapped. The last cancellations came a decade ago - a two-reactor station in Hartsville, Tenn., and another in Corinth, Miss.

Under consideration now is an unfinished reactor at the Watts Bar plant near Spring City, Tenn., and two at the Bellefonte plant near Hollywood, Ala. The Watts Bar reactor is 61 percent complete and the Bellefonte reactors are 88 percent and 57 percent complete.

Despite the utility's problems, a second reactor at Watts Bar - the only reactor currently under construction in the United States - should be completed, TVA has said.

That reactor, which has taken 22 years and cost more than $6 billion to get to its nearly finished stage, is scheduled to go into operation next fall.

TVA also must decide what to do with a long-shuttered reactor at Browns Ferry near Athens, Ala.

Another unit at Browns Ferry is scheduled to return to service in 1996. TVA has three reactors now running - a third reactor at Browns Ferry and the two- unit Sequoyah Nuclear Plant near Chattanooga.

In September, Crowell announced it was time to set a limit on future borrowing before it hits the $30 billion ceiling authorized by Congress in 1979.

Some 160 utilities and industries receive TVA power in the seven-state Tennessee Valley. TVA, owned by the federal government, serves nearly 8 million customers.