The American Ballet Theatre has no long-term contract with its artistic director and star dancer Mikhail Baryshnikov, sources at ABT disclosed tonight.

In what has turned out to be another startling development in ABT's sudden financial crisis and internal warfare, ABT sources said the ballet company's year-old announcement that Baryshnikov had signed a contract running through 1986 was incorrect.

ABT board president Charles McWhorter has declined to comment on any aspect of ABT's turmoil. Baryshnikov's spokesman could not be reached for comment.

The sources said executive committee chairman Melville Straus--who appears to be the leading candidate to become the new board chairman--was negotiating late tonight on the Baryshnikov matter. The ABT board is scheduled to meet Thursday.

If the contract problem is not ironed out quickly, sources said, several ABT board members who have tentatively pledged to personally guarantee large amounts of the estimated $2 million in bank loans that ABT needs for its upcoming season are expected to withdraw their pledges.

In the event that at least $1.5 million is not immediately secured, the sources said, the board is expected to shut the company down, probably causing a cancellation of ABT's scheduled four-week run in December at the Kennedy Center.

Some board members reached tonight were stunned to learn that the company had no contract with Baryshnikov, but others said Baryshnikov's verbal assurances that he would stay with ABT for some years to come should be adequate to satisfy worried members at Thursday's meeting and that a contract could be negotiated at a later date.

Baryshnikov's supporters have said he was eager to remain with ABT. He is scheduled to star in a film next spring and some board members have said they are worried he will be unable to devote sufficient time to administering ABT and to performing with the company.