A two-year clock started ticking yesterday on a proposed $149 million development near the Columbia Heights Metro station as an embattled city panel defended its award of exclusive development rights to two construction teams.

After delaying the award in a vain attempt to get a neighborhood consensus on the proposals, the Redevelopment Land Agency signed agreements for a Giant supermarket and retail stores to replace most of the interior of the historic Tivoli Theatre. Across 14th Street NW, a separate plan would produce a retail and entertainment complex, including movie theaters.

"We're very happy that we finally got to this point," said Joseph Horning III, representing the Tivoli Partners team, which has spent two years in hearings and interviews to advance its proposal. The other developer is DC-USA.

The parcels have remained blighted since the late 1960s. The city and the neighborhood hope the new developers finally bring commerce, culture and vitality back to the once-busy shopping corridor.

At the insistence of Mayor Anthony A. Williams (D) and members of the land agency board, the agreements announced yesterday set strict timetables for the developers--or the deals will be canceled. Within 90 days, they must submit development summaries outlining financing and other details. Within two years, construction must begin, with a one-year extension permitted to obtain zoning or historic preservation approvals.

But the signing sets the stage for another bit of political theater. Last week, the D.C. Council passed legislation giving the mayor authority to amend the deals, and the council the power to cancel them. It is authority the mayor does not want, as he attempts to remain above the contretemps.

"The mayor is planning to veto" the bill, Deputy Mayor Eric Price said yesterday. But he said Williams hopes the council will pull the bill back after reading the development agreements incorporating the timetables and community participation.

A sponsor of the bill, council member Jim Graham (D-Ward 1), said he is disappointed that the agreements do not include all the recommendations Williams made to the board.

Addressing preservation concerns about the Tivoli, Williams, in a letter released yesterday, wrote, "The developer should consider revising the site plan so the grocery . . . can proceed without immediate significant demolition impacts at the Tivoli."

"The part dealing with historic preservation has been left out of the exclusive right agreement," Graham said. "That's the heart of the controversy."

The land agency also issued a 12-page analysis of its choice of developers--its first extended defense of a decision that resulted in howls of objection from some who live in Columbia Heights. The board rejected another proposal supported by those residents that called for giving community groups the chance to raise money to renovate the Tivoli as a theater.

The land agency's analysis praised the winning developers for providing more minority participation, stronger financing and proposals with a better chance of success. The analysis said that the main losing developer--Forest City Enterprises--offered only sketchy plans for saving the Tivoli as a performing arts space.

But the agency's rationale persuaded few critics. Forest City had a substantial arrangement for minority participation, according to a source who did not want to be named but who is familiar with Millennium Development, the local minority partner of Forest City.

"They said [the Tivoli supermarket plan] was the most viable . . . proposal," added Geoffrey Griffis, a Columbia Heights resident who helped organize a charette, or brainstorming session, to get ideas from the community. "That's got to be the most absurd statement going."

Griffis and others said preservationists will file a lawsuit to block the project and make the supermarket plan, in their view, the least realistic proposal.

"It's obvious to me the fix was in from the beginning, and that enrages me," said David McIntire, another resident. "The charette was a charade."

CAPTION: A Giant supermarket and other stores are to replace the interior of the Tivoli Theatre on 14th Street NW under an agreement signed by a city panel yesterday.