Mayor Adrian M. Fenty, who supported the library when he was a member of the D.C. Council, said the hotel and retail stores are better suited for the vacant District-owned land, which once housed the city's convention center, between Ninth and 10th streets NW and New York Avenue and I Street. The city is leasing the land to the developer.

The hotel and retail, which a District official said will cost an estimated $150 million to build, will be part of a 10-acre site that District officials and the developer, Hines-Archstone, are promoting as a new downtown destination. The developer is building a mix of condominiums, offices, restaurants and shops, a half-acre park and a plaza on the remainder of the site.

"It is time we start calling this place what it is, our city center," Fenty (D) said in a statement, predicting that the parcel will "be a true retail and entertainment destination -- the heart and soul of our dynamic new downtown."

Williams (D) had promoted the proposed library building on a valuable downtown parcel as a powerful expression of the District's commitment to its residents. But his plan, which he proposed toward the end of his time in office, failed to win support from the D.C. Council.

Fenty said the District is looking at a number of sites for a new central library, but he declined to specify where. The District, Fenty said, has not decided whether to build a facility or renovate the system's headquarters, the Martin Luther King Jr. Memorial Library at Ninth and G streets NW, which was designed by German architect Ludwig Mies van der Rohe.

Council member Jack Evans (D-Ward 2), whose district includes the former convention center site, characterized Williams's vision for a new library on the property as a "terrible idea."

"It's too valuable a piece of property," Evans said. He described the proposed hotel as "another exciting opportunity for downtown."

Williams did not return a call seeking comment.

John W. Hill Jr., president of the board of library trustees, had supported Williams's library project. But he said his interest waned as District officials reduced the amount of land they would devote to the building. Now, he said, the library system is exploring other options, including opening a customer services center at the Carnegie Library and moving administrative employees to offices east of the Anacostia River.

"We're excited about looking at these other opportunities," Hill said.

The proposed hotel will add 400 rooms to the neighborhood slated for the convention center hotel, a 1,150-room complex to be built by Marriott International and RLJ Development.

The District has 29,000 hotel rooms, but officials want more, said Victoria Isley, a spokeswoman for Destination DC, which markets the District and the convention center. "There's a need for more hotel rooms, and definitely more near the convention center, which is what's on the horizon," she said.

Hines-Archstone plans to include on the site what officials described as "large-format retail," a department store such as Bloomingdale's or Nordstrom. William Alsup III, a Hines-Archstone vice president, said the developer hopes to announce the project's retail component within six months.

The announcement about the hotel comes as a tightening credit market has slowed construction projects across the region.

However, many District projects being built now started before the slowdown.

Developers conceiving projects, such as the old convention center site or Poplar Point, are in the design phase and are not yet seeking financing.

Less than two blocks from the Walter E. Washington Convention Center, the site of the proposed new hotel is among the last vacant parcels in the city's central core and provides District officials the chance to further transform downtown.

When it is built, District officials say, the development on the old convention center site will help complete their vision of a downtown that thrives beyond 9 a.m. to 5 p.m. office hours with a blend of shoppers, office workers, residents and tourists visiting shops, restaurants, clubs and museums.

"It's not a daytime city anymore. It's got a nighttime economy," said Richard Bradley, executive director of the Downtown DC Business Improvement District, a nonprofit organization that promotes revitalization.