A key Senate subcommittee chairman severely criticized the District of Columbia's revised plans for the proposed Washington Civic Center yesterday, saying that most of the privately financed spinoff development being touted by the city does not meet congressional requirements.

"Where's the rest of it?" was the first reaction of Sen. Patrick Leahy (D-Vt.), according to an aide to the senator, whose Senate Appropriations District subcommittee must give final approval to the center.

Leahy was said to be particularly disturbed to find that a list of spinoff development projects sent to him by city officials appeared to be "quite shallow" and contained some projects that are expected to be built regardless of whether the controversial center is constructed.

The Leahy aide said the city's list - which detailed $42 million worth of projects - seemed actually to provide only $2.9 million to $5.6 million of the necessary $7.5 million in new tax revenues that is to be used to finance the facility's mortgage and operating costs.

Leahy made such spinoff development commitments a condition for approval of the complex, which is proposed for a three-block site just southwest of Mount Vernon Square bounded by New York Avenue and H, 9th and 11th streets NW.

The Leahy aide said yesterday the senator would hold hearings, if possible before the Oct. 14 adjournment of Congress, to determine which commitments for additional spinoff developments are genuine - that is, related to the center - and which do not qualify for inclusion in the overall financing picture for the facility.

At the direction of Leahy and his counterpart in the House, Rep. William Natcher (D-Ky.), city officials spent the summer revising an earlier proposal to build a $110 million center. In mid-August they detailed new plans for a scaled-down facility that they say would cost $99 million and be partly financed by a hotel occupancy tax and a surtax on corporate businesses.

But it was not until late Monday that Leahy finally got a look at the central element of the revised center proposal, namely the specific commitments by private developers to build center-related hotel, restaurant and retail projects that would generate new city tax revenues to make the center economically feasible and lessen the tax burden on D.C. residents.

Under the terms of a joint House-Senate agreement worked out by the respective subcommittees in May, no funds to build the center will be released until the business sector has made firm commitments to develop new projects directly related to the center's construction.

Based on a preliminary review of the 39 projects named on the city's spinoff commitment list, only two to four proposed developments clearly meet the conditions set out in the congressional agreement, according to a Leahy aide.

Ben Gilbert, director of the D.C. Municipal Planning Office and a key member of the special task force that put the revised center proposal together, said yesterday the city had demonstrated that the project "won't become a liability on D.C. taxpayers, which has always been Sen. Leahy's main concern."

Even if some of the spinoff projects eventually are discounted, Gilbert said, "we've got commitments to spare" to pay for the estimated $7.6 million operating and loan repayment costs associated with building the center.

Knox Banner, executive director of the D.C. Office of Business and Economic Development, which specifically concerned itself with lining up private development commitments, did not return a reporter's telephone call to discuss the various projects.

The city's list of projects is drawn from various "letters of commitment" from private developers, copies of which were obtained by The Washington Post. They include numerous developments that have been planned - and will go ahead - regardless of whether the center is built.

For example, several proposals to redevelop the old Willard Hotel, the National Press Club building site and property at 12th and G streets NW were included even though private developers already are actively competing to build at all three sites.

One project, proposed expansion of the Quality Inn near the Capital, clearly is contingent on approval of the center, according to a letter submitted by an official of the firm that owns the hotel.

Another, proposed renovation of the old Ambassador Hotel at 14th and K streets NW, appears to be already in the planning stages.

"If the center does not proceed, we would still hope to be able to develop some commercial space but fear that the timing might be delayed . . ." according to a letter from an official of the development firm.

Several prospective developers say construction of the convention center would help them obtain financing for their projects if and when they decided to build them.

City officials have consistently maintained that it is difficult to line up specific development commitments because of uncertainties surrounding the center proposal. They argue, however, that construction of the center would attract new visitors and employment opportunities and be a crucial contribution to efforts to revitalize the old downtown west of 15th Street NW.

Opponents of the project have complained that it amounts to a subsidy for the business community and, in any case, should be voted up or down by residents in a referendum.