The General Services Administration says that it will sell a block of prime federal property in downtown San Francisco to that city's Redevelopment Agency if Congress will affirm that no one at the agency did anything "illegal or improper" in connection with the $17.4 million sale.

But Rep. Elliott Levitas (D-Ga.), the chairman of one of two congressional subcommittees that raised the question of propriety last summer, wants the sale held up until his staff can complete its investigation this spring.

Levitas said a preliminary investigation indicated that it would have been better for the GSA to trade the federal site at 49 Fourth Street for an unneeded parcel of city property since there is a pressing need to build a new facility in San Francisco.

Last July, the GSA was ready to sell the property when published accounts alleged the deal was being made because Marriott Corp.--a major Republican Party corporate supporter--had put pressure on GSA Administrator Gerald P. Carmen.

Marriott and real estate developers Olympia & York of Toronto are in the final stages of negotiations with the redevelopment agency for a $1 billion contract for design and construction of the 22-acre Yerba Buena Gardens. It will include a convention center hotel, an office building, and various recreational and commercial facilities. The Gardens are the centerpiece of an 87-acre redevelopment project that surrounds the city's new George R. Moscone Convention Center complex.

As it turned out, Carmen already had decided to sell the land to the city, but because the redevelopment agency didn't know that, it asked Marriott to help lobby the GSA.

Levitas said Monday that the Marriott situation was a "separate matter" that he did not think had a bearing on the decision to continue the investigation into why the GSA decided to conduct a negotiated sale rather than to trade properties. "Marriott would end up with the property either way," Levitas said.

The GSA had put the deal on the back burner after last year's hearing, but, just before Christmas, San Francisco Mayor Dianne Feinstein told the GSA that she needed a decision by Jan. 7.

"Further delay . . . could jeopardize the entire development program," Feinstein wrote.

In response, Carmen told Congress Monday that he is "still convinced that the sale of the property is in the best interest of the government." However, Carmen said, "I will not go forward to accept the offer of the Redevelopment Agency . . . until such time as I receive the . . . subcommittees' determination that neither I nor anyone in this agency has taken an illegal or improper action in proposing to accept the offer to purchase."

Concerned about the image of his agency, Carmen added: "If we cannot resolve this issue within a reasonable time, we will proceed to a public sale, which by the nature of the procedure should eliminate any questions of legality or propriety."