WASHINGTON -- Defense Secretary William Cohen told Congress Wednesday that the administration might commit a "relatively small" U.S. ground force to Kosovo but only if a firm peace agreement is reached between warring factions.

Other NATO members should make up the majority of such a force, he said.Pressed by senators on the likely size of the U.S. contingent, Gen. Henry Shelton, chairman of the Joint Chiefs of Staff, suggested 2,000 to 4,000 U.S. troops might be required if NATO decides on an overall force of 20,000.

But, he told the Senate Armed Services Committee, those numbers were hypothetical.

"The numbers are still being worked. The numbers that we would be asked to give would depend on what the final numbers are," he said.

Still, Shelton told the panel he had "no doubt" that the United States would be asked to contribute such a force.

Kosovo's ethnic Albanian rebels have agreed to participate in peace talks demanded by the United States and NATO allies as pressure increased on Serbia's hard-line government to join the talks. NATO has threatened airstrikes if Serbia and the rebels aren't talking by Saturday and closing a peace deal by Feb. 19 under talks organized by the United States and five European powers.

"There would have to be a real agreement, not something that is illusory, not something that has the appearance of being an agreement, but would allow our people -- should we have people on the ground -- to be caught in the crossfire between the warring and ethnic factions," Cohen testified.

His testimony came a day after CIA Director George Tenet told the same panel that NATO troops will be needed to prevent wider warfare between rival factions in Kosovo even if a peace agreement is reached.

"I cannot and would not support any notion of NATO trying to make an intrusive invasion into Kosovo to establish a peace or to make a peace. That would be unwise in my judgment," Cohen said.

Cohen told the panel he could support sending U.S. troops to Kosovo only if an agreement providing for a cease-fire of from three to five years was put in place.