City officials and a team of developers have agreed to build a retail and residential complex and a new public library on the site of the old Washington Convention Center -- but the deal would rule out building a music museum, a major hotel or a new convention hall on the land.

With the agreement, Mayor Anthony A. Williams (D) has set out his vision of what should be on the $300 million site, but to execute it, he will have to navigate a jumble of competing interests that disagree with certain elements and may push for changes.

Some members of the D.C. Council, which must approve the plan, think a new public library would be too expensive. Others favor putting a big hotel on the convention center site, not on a more expensive piece of privately owned land two blocks north.

Members of the Washington Convention Center Authority and some key council members want the site to include underground space for future expansion of the new convention center two blocks away. An influential group of business leaders, the Federal City Council, is unlikely to give up on its plans to build a National Music Center, with a museum and auditoriums, as part of the project. "We're going to be doing a lot of outreach in the next couple of months," said Eric W. Price, the deputy mayor for planning and economic development. He said he plans a series of meetings with council members and their staffs in an effort to sell them on the mayor's approach.

In November, Williams named a development team, led by Hines Interests LP, to redevelop the 10.5-acre site of the vacant old convention center, bounded by H Street NW, New York Avenue, Ninth and 11th streets. For the past eight months, Williams's staff has been negotiating with the builders exactly what the project would include and how it would be paid for, with the final agreement reached this month. The agreement could be revised substantially, though, as the administration tries to get the package through the D.C. Council.

"We believe it is now very important that the mayor and city council sit down and decide on the public use components so that we can move forward with a master plan," said William B. Alsup III, who heads Washington area operations for Hines Interests.

Development of the site, the mayor's aides and foes agree, could reshape downtown Washington, creating a vibrant new symbolic center of the city and extensive new housing. The complete project could cost an estimated $800 million, paid for by the developers. In the best of circumstances, it is unlikely to be finished until 2010.

Aides to Williams declined to release a copy of the "exclusive rights agreement" with the Hines group because the administration does not plan to present it to the council for consideration until the fall, and it could be revised in the meantime to reach a compromise. But three sources who have seen the lengthy document described it in detail.

The agreement calls for at least 1,200 apartments, with 20 percent reserved for those with low to moderate incomes. There would be at least 300,000 square feet of retail space, grouped around a public square where the developer would fund musical performances and other programs. The city would build a new library on the site, funding it by putting a modest amount of office space or a small hotel on top of the library, much of which would be underground.

The development team would enter a 99-year ground lease with the city and pay a fixed, multimillion-dollar rent each year for use of the land. The exact size of that payment would be determined by market conditions once the project is ready to proceed. The city also would be entitled to one-fourth of the project's profits beyond the developers' standard economic return. After 99 years, the city would own the project outright.

Excluded from the mayor's plan, as negotiated with the developers, is the National Music Center and Museum, a proposal created by influential civic leaders and musicians working with the Library of Congress and the Smithsonian Institution. Kenneth R. Sparks, executive vice president of the Federal City Council and a driving force behind the music center concept, declined to comment yesterday afternoon.

"In our conversations with the [D.C.] Council up until now, there hasn't been strong support to subsidize a cultural facility," said Deputy Mayor Price. "They were clear they wanted to see us maximize economic value to the extent we could, given other public policy objectives."

Price called the music museum "a salvageable idea, even if there isn't the support to have it on this site."

Some on the D.C. Council, including Chairman Linda W. Cropp (D) and Finance Committee Chairman Jack Evans (D-Ward 2), oppose a library on the site. "This is the most valuable piece of land on the East Coast," said Cropp. "Why put a non-revenue-generating project there?"

"The library could go somewhere else," said Economic Development Committee Chairman Harold Brazil (D-At Large).

Price said putting commercial real estate on top of the library would not only fund a new central library but also produce revenue to support dilapidated branch libraries in other D.C. neighborhoods.

Perhaps most contentious is the question of expansion space for the new Washington Convention Center, which opened last year two blocks away from the old site. The new center is hemmed in, with few options to expand if demand for convention space grows substantially. People close to the Washington Convention Center Authority have argued to council members that underground space on the old site should be reserved for expansion. Officially, the quasi-public convention agency is waiting for a consultant's study to be completed next month before taking a position, said Convention Center Authority spokesman Tony Robinson.

If the authority openly pursues an underground exhibition hall on the old site, it will have some allies on the council. "When we made the decision to build the new convention center at its location, it was built there only because we could use the old convention center for expansion," said Cropp. "That's why I voted for it."

A final moving part is a big, new hotel that the Williams administration proposes, using public money, on land just west of the new convention center. The "headquarters" hotel, to be managed by Marriott and built on land now owned by developer Kingdon Gould III, would have about 1,200 rooms. A prominent local architect proposed this spring that the hotel be built on the city-owned old convention center site instead, an idea the mayor's aides firmly rejected -- but which some D.C. Council members were more open to.

Still, some on the council put the greatest priority on moving things along. "The mayor needs to do some work to get some of my colleagues in line with what is a good plan," said Brazil.

"This is a good plan. It's a good bid. Let's be on with it. We'll be here 10 years from now talking about the same things if we don't get going."