Three of the nation's largest private hospital chains are preparing bids to take over George Washington University Hospital -- a transaction that, when completed next year, could nearly double GWU's endowment.

Barry Jagoda, a university spokesman, said Hospital Corp. of America, American Medical International Inc. and National Medical Enterprises Inc. had answered GWU's request for proposals for a takeover of the 511-bed hospital, one of the area's largest. Teams from the three companies will visit the hospital over the next few weeks, and the bids are expected by late May.

The fourth company invited by GWU to bid, Humana Inc., of Louisville, declined to make an offer, Jagoda said. Humana apparently was unwilling to give GWU as much control of the hospital as university officials desire. A Humana spokesman, Robert Irvine, would say only that "We looked at it and felt that at this time it didn't seem to be a good fit."

GWU put the hospital on the block earlier this year, saying it could not afford to keep operating the facility because it needs $30 million in major improvements.

Jagoda said yesterday the university is likely to sell the facility, an action that by some accounts could bring in $125 million, making GWU's endowment about $275 million.

GWU's conditions for bidders included that they operate at least 50 other hospitals, including at least one the size of GWU Hospital; that the hospital be governed after the sale by a GWU-controlled board; that they make operating and capital investments in the facility; that the current medical staff organization and rules be continued, and that the existing nonacademic staff be retained for at least a year.