James C. Fletcher, the nominee to be administrator of the National Aeronautics and Space Administration, received more than $45,375 in directors' fees last year and owns $15,000 to $50,000 worth of stock in an aerospace firm that is lobbying the agency to build a privately financed shuttle orbiter to replace the destroyed Challenger, according to financial disclosure statements released yesterday.

The ownership interest in Astrotech International Corp. is among Fletcher's financial holdings worth between $1.7 million and $4.49 million, including several other aerospace interests that he pledged in a letter to sell once he takes office to avoid any conflicts of interest.

An Astrotech subsidiary, General Space Corp., has been lobbying NASA in recent weeks on behalf of a controversial proposal to privately finance a new $2 billion shuttle orbiter, then lease it to the space agency for a profit. Astrotech's chairman, Willard Rockwell, has said he has met with White House chief of staff Donald T. Regan and acting NASA adminstrator William R. Graham about the proposal.

Fletcher, who listed himself as a vice chairman of General Space and a director of Astrotech, said in his letter that he would sell his interests in Astrotech and disqualify himself from matters affecting the firm. But some congressional staffers have questioned whether he could completely remove himself from decisions involving so basic an issue as a new orbiter.

Fletcher also has pledged to sell interests in Fairchild Industries, which had been a NASA contractor for a space platform, and Burroughs Corp., which supplies computer software to the agency.

Fletcher's nomination, announced March 6, has raised concern on Capitol Hill because of the time it has taken to submit his financial disclosure and related papers. He is scheduled to appear before the Senate Commerce, Science and Transportation Committee today. Some staffers said they expect him to be confirmed quickly.