The District government is making a major effort to lure a Bloomingdale's department store to the city by offering a developer extra construction rights in exchange for his paying at least $2.5 million to the trendy retailer to persuade it to locate in old downtown.

Curtis R. McClinton Jr., the city's deputy mayor for economic development, said final details have yet to be negotiated on the deal, but predicted that the financial arrangements among Bloomingdale's, two developers, the city and others could be completed by September.

Under the deal, developer Nathan Landow said, the city would give him and developer John Akridge the right to build an extra 110,000 square feet of retail and office space on the block bounded by 12th, 13th, F and G streets NW, above the Metro Center subway stop.

In exchange, Landow said, he has offered to make the $2.5 million payment to Bloomingdale's "as an incentive to bring them into the project."

The commercial and office complex, if eventually built, would be the latest in a string of major retail and office face lifts in the city's deteriorated old downtown that for years was bypassed by major retailers who built their stores in suburban malls that attracted shoppers away from the District. Bloomingdale's, with stores at the Tysons Corner and White Flint shopping malls, was one retailer that looked first to the Washington suburbs when it expanded from its New York base.

Landow and McClinton said Bloomingdale's, which the city has unsuccessfully courted in the past, has sought a $6 million payment to open a store in the District.

"We've made this offer and hope Bloomingdale's will accept," Landow said. "We don't know." Landow said Bloomingdale's officials have not responded, but "the word at the last meeting was that Bloomingdale's was flexible." Store officials declined to comment. McClinton said the store chain has "shown very strong interest, subject to the economics."

The deputy mayor described the city's offer as providing "substantial economic incentives both to the developer and the retailer. Our proposal closed the gap. It makes it more equitable to both parties."

The city owns the northeast corner of the block and awarded the development rights to Landow and his partners several years ago. Akridge said he owns or controls the western half of the block. Landow said he has "tentative agreements" to purchase the remainder of the block.

Under the $150 million construction plan, Landow and Akridge said they would clear the small, deteriorating stores on the block, while in some manner preserving the Homer Building, a 13th Street office structure that is a local landmark.

Landow said a three-story Bloomingdale's store would be built, with two levels underground. In addition, 40 to 50 smaller retail shops with an entrance directly into the Metro Center subway station would be constructed, as well as a 700,000-square foot office building and a two-floor garage.

Landow said that because of existing leases on the property, construction could not start for 12 months after the deal is completed with Bloomingdale's, roughly the fall of 1986 at the earliest. He said it would take 12 to 18 months to build the store, a total of two years to complete the overall complex.

A Hecht's department store is nearing completion across G Street from the prospective Bloomingdale's site, while two of Hecht's competitors, Woodward & Lothrop and Garfinckel's, have embarked on multi-million dollar renovation projects at their nearby locations. In addition, a large mall called The Shops at National Place was recently completed.

Bloomingdale's has looked at several possible downtown locations in the past, including at the Washington Square office and restaurant complex at Connecticut Avenue and L Street NW and at the Willard Hotel, 14th and F Streets NW. But the latest effort appears to be the most serious and concerted.

One official of the Greater Washington Board of Trade said that "what the city has to offer now is the revitalization of downtown. That's dramatically different than what it had to offer last time around when everything was just on paper.

"There were still a lot of ifs to Hecht's new store, still a lot of ifs to the hotel now under construction on Woodies' north block and still a lot of ifs on the [reconstruction of the] Willard, the Marriott [hotel] and The Shops," he said. "Now there are people at The Shops. You can count them."