The future of downtown Washington will be determined to a large extent by the recommendations made last week by the Mayor's Downtown Committee.

An ambitious (and only a little unrealistic) prescription for downtown development through the year 2000 has been prepared by the panel headed by banker Luther Hodges, Jr. with the aid of city planning officials.

In the next 20 years, the District will have the opportunity to create 95,000 new jobs and a world-class downtown in the 658 acres bounded by Pennsylvania Avenue on the south, 15th Street on the west, M Street on the north and North Capitol on the east.

The strongest aspect of the plan is its commitment to rebuilding the city's retail core into a major regional shopping center that will enable the District to match the concentration and quality of stores at Tysons Corner, Springfield or Montgomery malls.

Construction of new office buildings will provide the momentum for the massive revitalization effort, continuing at a pace that could average close to a square block of new buildings every year.

The economics of office construction are so attractive that without government intervention the entire neighborhood could be officed over, squeezing out the housing, stores, theaters and restaurants needed to create the "living downtown" that everyone agrees should be the goal.

Housing is the weakest link in the chain of events leading to a living downtown. Barely 6,000 people live downtown now, 30 percent fewer than a decade ago. Ideally, the population ought to grow to 15,000 people, a concentration about the size of the adjoining Shaw neighborhood and nearly twice as many people as live in Georgetown.

But only two-thirds of the additional housing needed for that growth will be built unless the government provides either direct subsidies or some other aid to enable apartments to compete with offices for scarce land, the study warns. With the Pennsylvania Avenue Development Corp. abandoning its commitment to subsidized housing in the part of downtown it is rebuilding and the Reagan administration bent on cutting federal aid, the housing target is not likely to be hit.

While the mayor's committee plan is embarrassingly short of answers to the housing question, it draws a distinct blueprint for revitalizing the retail core.

"No topic in the downtown planning effort has involved more discussion than the form and compositon of the future retail core," the plan notes.

"In terms of overall quality of space and arrangement the retail pattern in downtown is out of date," the committee concluded. The prescription is for two or three new department stores grouped together in a smaller but better shopping district.

Stretching three-fifths of a mile along F Street from Garfinckel's on 14th Street to The Hecht Co. on 7th Street, the main shopping strip is simply too strung out.

People won't walk that far, so the plan calls for pruning two blocks and 1,500 feet off the central retail core. The anchor for the east end of F Street would become the Woodward & Lothrop store between 9th and 10th, F and G Streets.

Hecht's is already trying to leapfrog into the midst of that core by negotiating to build a new store in the long-awaited development atop the Metro Center subway station on the north side of G Street between 12th and 13th Streets. Bloomingdale's, too, is looking at Metro Center.

The downtown committee for the first time calls for making room for another department store and a major retail development south of Metro Center, between F and G, 12th and 13th Streets.

"Economic studies have indicated that the addition of a fourth department store at this location would mean a major jump in the retail drawing power of the entire retail core, increasing retail sales levels and attracting other retail establishments," the committee said. A fifth department store might be built between 12th and 13th streets on the south side of F Street, the report adds.

Since the city's Redevelopment Land Agency already owns the Metro Center property, it can easily accomplish the goal of moving Hecht's or another department store to that site. Bringing the fourth department store to one of the neighboring blocks will be more difficult, but should become a top priority for downtown planners.

The plan calls for maintaining F Street as "the primary retail focus in downtown" and urges that zoning laws be changed to require "continuous, active retail uses along both sides of F and G streets within the retail core."

Though several new retail developments are envisioned by the committee, the total amount of store space would grow only slightly, from the present 5.7 million square feet to 5.9 million square feet. But only 2.3 million feet of existing space should remain; the rest needs to be replaced by new, more productive stores.

While recommending a concentrated retail core between Garfinckel's and Woodies, the committee does not write off the 7th Street shopping corridor.

Seventh Street should become the Harborplace or Quincy Market of Washington, a "festival marketplace" with small shops, eating and drinking establishments and specialized stores running from Pennsylvania Avenue to Chinatown, including a new development on the underutilized land atop the Gallery Place subway station.

Another creative idea endorsed by the committee is to set up some sort of special shuttle trolley system in the retail core. Whether an old-fashioned streetcar with tracks and overhead wire or a newfangled battery-powered bus, the shuttle ought to be "fun, easy to identify and easy to get on and off."

Street vending also ought to be expanded downtown, the panel urged, endorsing the idea that prestige merchants and push carts both add to the ambiance and economy of the city.

The retail revitalization endorsed by the panel would make downtown D.C. a vital and varied urban shopping center, a retail district more dynamic than any in the country save New York or Chicago.

But the most important feature of the plan is that it is do-able. Historic preservation, housing, transportation and zoning issues have to be resolved, but none of these problems is insurmountable. The Downtown Committee has given the District a taste of 21st century Washington, a golden apple within the grasp of a growing city.