Downtown Washington, a business center that almost died a decade ago, today is on the verge of a spectacular rebirth.

Lured by Metro, the Pennsylvania Avenue Development Corp. and the Convention Center private developers are moving east of 15th Street NW., the symbolic boundary between the booning western office core and the blighted eastern retail center

The city's insatiable appetite for new offices, stores and apartments has consumed most of the land west of 15th Street, leaving only the old east downtown - from 15th Street NW to the Center Leg Freeway, between Pennsylvania Avenue and Massachusetts Avenue.

If all the projects now on the drawing boards for the neighborhood are built, more than $1 billion will be poured into the District of Columbia's downtown.

"In the first five years of the 1980s, you are going to see the transformation of the commercial core of this city," predicts Ben Gilbert, the city's planning director.

How the downtown will be transformed and who will transform it will be decided in the next few months.

At the end of July, the Pennsylvania Avenue Development Corp. (PADC) will receive proposals from would be developers of two pivitol projects - renovation of the Willard Hotel and redevelopment of the blocks surrounding the National Press Building at 14th and F Streets NW.

On the back of the Press Building block, the Palace Theatre has just been demolished and work is now starting on the first new building in the PADC area, a new headquarters for the National League of Cities at the north west corner of 13th and E Streets NW. PADC will soon raze the vacant Kanns department store, one of the avenue's monumental eyesores.

The Redevelopment Land Agency already has received preliminary proposals from three developers who want to spend between $80 million and $250 million rebuilding the properties atop the Metro Center subway station, a two-and-one-half-block strip of G Street NW from 11th Street west past 13th Street. A decision on that project will come by fall.

Garfinckets and developer Oliver T. Carr are making final plans for the $50 million reconstruction of the block around Garfinckets' store, and Woodward & Lothrop is taking the first steps toward rebuilding the block north of its downtown flagship, a project of similar scale.

The District government's capital improvements budget for this year includes funds for a new office building on the eastern fringe of downtown at Fourth and E Streets, and for the downtown campus of the University of the District of Columbia on four blocks north of Mount Vernon Square. By the end of the summer, work will be under way on 300 units of subsidized at housing on the site of the old Wax Museum, 5th and K Streets NW.

And by fall a congressional committee is expected to take a final look at the convention center and decide whether it will bring the city more in revenues than it will cost to build. It convention center backers can convince Sen. Patrick Leahy (R-Vt.) that the project is economically sound construction could start within two years on the site, south of New York Avenue between 9th and 11th streets NW.

If the convention center is shut down, it will not end the resurgence of downtown, but it will alter drastically the tone and timetable for the neighborhood.

Explained J. Kirk White, deputy director of the municipal planning office. "Without the civic center, it would mean the east downtown would become more like the west" - eight-story office buildings with small shops and restaurants on the lower floors.

If the convention center is built added John Fondersmith, chief of the planning department's special projects division. "It will drastically speed the rate of development we want to happen and it will shift the mix of development toward hotels and retail that we would not otherwise get."

That shift would have important economic implications for the city, helping produce what White called "a balanced economy."

Office buildings yield property taxes and white collar jobs, the planners explained. Hotels produce not only property taxes, but also hotel room taxes and additional income from levis on the food and drink visitors consume. Hotels also create more blue collar jobs and more entry-level positions for young unskilled workers, who have the highest unemployment rate in the city.

City officials and other convention center backers are putting together a list of prospective downtown developments to satisfy congressional demands that the center pay for its operating deficit and financing charges - a $7 million-a-year or $8 million-a-year boost in tax revenues.

While they are confident they can meet the demand, they fear congressional quibbling over what new construction will count toward the convention center quota Projects that would be built regardless of whether the convention center goes don't count with Congress.

Because of the uncertainty about the center and because of the fear that projefts announced now might not be included in the quota, some developers are holding back on final details of their projects.

The press building project long discussed by Atlanta architect builder John Portman probably will be primarily an office complex with a small hotel if the convention center is not built. With the center, a big convention hotels is likely.

A hotel also probably will be part of the Garfinckel block if the convention center goes, otherwise, that development will be mostly office and retail. The extent of retail development will depend on the convention center, without it. There may be difficulty attracting another big specialty store to share the block with Garfinckel's.

A hotel is also part of the mixture of uses the Redevelopment Land Agency wants for the Metro Center site but, as builder Carr stressed in a recent meeting with RLA board members, without the convention center there will be little demand for a hotel at Metro Center.

Carr is one of three builders in the running for the Metro Center work who will submit formal proposals for the site later this month Carr's version of the project would total 1.8 million square feet of new construction, with about 500,000 square feet of new retail stores, plus offices, apartments and maybe a hotel.

Bethesda builder Nathan Landow has suggested a project about the same size, but with fewer stores, utilizing large setbacks and lower-level shopping arcades to avoid the "K" Street Look" that planners adamantly want to avoid in the east downtown.

The most ambitious proposal for G Street has been made by Western Development Corp. in partnership with Rockefeller Center, which called for putting a massive retail-office structure half again as big as the other developers suggested. Incorporating both a hotel and a major department store, the Western Development proposal would use the four city-owned tracs on G Street plus the adjacent north block of Woodward & Lothrop.

Woodies is willing to consider proposals for redeveloping the land on which its old store sits but has made no commitments said William McDonald vice president for sales promotion. The department store owns the old store, the adjacent parking ramp and some other property on the block, which would be just one block from the convention center.

He said Woodward & Lothrop will need part of any new building for the offices, support facilities and selling space now in the old building, and would prefer extensive retail development for the rest of the block.

Several major retailers have been investigating downtown store sites, among them real estate specialists for Federated Department Stores, the company that owns Bloomingdales, which already has stores at White Flint and Tysons Corner, and also the parent of L. Magnin, a California special chain about to open at White Flint.

Although a downtown Bloomingdales, if it is built, would most likely be in the project planned for the southwest corner of Connecticut Avenue and L Street NW. Federated's Magnin is a potential neighbor for Garfinckel's or Woodies.

Counting on and contributing to the resurgance of downtown shopping. Woodward & Lothrop is in the midst of a $6 million renovation job on its flagship, redoing the big store floor by floor. McDonald credits the Metro subway - with an entrance in the store's basement - with halting the long-term slide in downtown retail sales.

Developers agree that having its own subway entrance is a big appeal of RLA's G Street property and of the land above the Gallery Place subway station, which is also available from RLA. The Metro entry sites will be the first to be developed in the east downtown, not only because of their subway access but alos because they already have been bought and readied for development by government agencies.

Besides Metro and the convention center, the third government factor in the downtown development equation is the Pennsylvania Avenue Development Corp., with its congressional mandate to rebuild 20 blocks along the north side of the avenue between the White House and the Capitol.

The agency's plan is to build 1,500 units of housing along the blocks east of the new Federal Bureau of Investigation building, and offices, hotels and stores west of there. By buying the land. Clearing it and turning it over to builders ready to develop, PADC can speed and simplify the reconstruction process, explained Rita Abraham, the agency's press officer.

PADC is expected to send about $130 million on public facilities and planning in the process, stimulating $500 million in privae private investment.

This year PADC is pouring $20 million into street improvements, including new sidewalks, street furniture, plantings and lightings along Pennsylvania Avenue and the cross streets, and will spend $60 million in the next seven years on streets and sidewalks.

In the woks is a proposal to turn the vacant Lansburgh store into a multifloor mini-mall with arts and crafts shops and temporary quarters for many of the small stores that will have to be relocated when existing buildings are torn down for new construction.

PADC's first commercial project is about to begin, an $18 million office building on the back of the press building site. The east downtown will probably bloom first in that neighborhood, with the press building project, the Willard and the Garnfinckel's block all completed within five years, the planning theorize.

Commercial development will move down the avenue to the FBI building next, and the massive housing projects planned by PADC for the east end of the avenue are as much as 10 years from completion. The Canadian government is holding a design competition for its new chancery, to be built within a decade on the north side of Pennsylvania between 5th and 6th Streets NW.

The convention center could open within five years, with the first construction on the G Street Metro Center site completed by then and development of Metro Center finished within a decade.

The long-range plans call for building more housing in the neighborhood adjoining downtown north of Massachusetts Avenue and east of the University of the District of Columbia campus. The 300 subsidized housing units soon to be built on the Wax Museum property are the first of a planned 1,000-unit project mixing subsidized and nonsubsidized units.

These housing project, plus thos sought by PADC and RLA, are supposed to bring more people into the streets of downtown, not only to shop, but also to create the street activity that planners have learned is essential for successful urban living.