After two-and-a-half years of operation, the Metro subway is having a mixed but potentially profound impact on the economic and commercial life of the Washington Area.

"Something," said real estate executive Raymond Kass, "has happened to downtown, and I don't know what else it could be but Metro."

Although the effects of Metro are uneven - with some merchants and business people finding little or no change in their sales - others already see long-range benefits from the subway system, especially for Washington.

"I thought that Metro was an enormous boondoggle," real estate developer Leonard Abel said in an interview. "But now I think that it will be as important to the salvation of the city as the Beltway was to the development of the suburbs."

The most immediate and measurable impact that can be directly attributed to Metro has come from the increased hours of operation in the evenings, since Metro expanded its service on Sept. 25 from its previous 8 p.m. closing to midnight, and its Saturday operation, which began Sept. 30.

Woodward Lothrop, which has an entrance from the Metro Center stop directly into its main, downtown store, reports an increase of about 10 per cent on Saturdays over last year since Metro began operations on Saturdays.

According to William McDonald, vice president for marketing of Woodward/Lothrop, the traffic coming through the Metro Center entrance into the store is equivalent to what the store was receiving last year on an average Christmas shopping day - the store's busiest season.

McDonald said he expects the extension of Metro to New Carrolton to add another 7 percent to 8 percent every day "through our doors."

Metro officials estimate the 60,000 to 70,000 riders use the subway on Saturdays. The average week night ridership has been about 9.50 persons - in both instances about what Metro officials had projected.

The effect on business from extension of evening operating hours by the subway is more difficult to measure. McDonald said, but the overall impact of Metro is clear. "Keep in mind," he said, "this store all of this year has had two floors - 80,000 square feet - torn up, and yet we have done a volume in excess of last year."

Last year was a good, but not a great year for Woodward/Lothrop, so the increase with a major portion of the store torn up for renovations is all the more startling, McDonald said. "You've got to believe there's a material factor going on and the only thing we can cite is metro."

Interviews with evening shoppers by The Washington Post found nearly uniform praise for the system's convenience. Ralph Nappi, an Old Town Alexandria resident, said in downtown Washington, "If the subway was not here, I would not be here. I believe in public transportation. I work downtown at 17th and K streets, and I came here from work. I find the selection to be better downtown than in the malls, where they often don't have your size. It's just as easy to use the subway and come downtown to get what you want than going to the malls."

James M. Reed, of Springfield, who had come downtown for an evening movie, said he drove to Rosslyn, parked his car and then he and his wife took Metro to Dupont Circle to see the film. Although not a regular rider, Reed said, he finds that Metro "makes it more convenient to go places you would like to visit, but don't want to fight the inconveniences of driving."

Crystal City, now toward the far end of the southwestern leg of Metro's Blue line, also has prospered because of Metro. Merchants in the Virginia complex universally reported increased business in the evenings and on Saturdays, all attributable to Metro.

Crystal City's underground mall, which includes a number of small shops, boutinques, some larger stores and eating spots, was designed to capitalize on the proximity of the Metro. Stores are open every weekend night until 9 p.m. and on Saturday until 6 p.m.

According to Allen Peterson, manager of Tropica, a plant and flower shop in Crystal Square, business has increased 40 percent since the Metro Blue Line opened in July 1977, bringing passengersto and from the District of Columbia.

"Since they've opened," Peterson said, "there's a different mix of people coming in - not just office workers, but parents and children." Peterson said he is carrying a "wider range of stuff" now as a result of the changed business, including larger plants, as well as "more of everything."

Saturdays, according to George Cholakian, manager of the Metro Camera Store, "have been very good," with more than a 50 percent increase in business since Metro began its Saturday operation.

Metro has brought some problems, too. Mareen Rolls, manager of the Spectacle Shop in the Crystal Mall, said the arrival of Metro has brought "a greater amount of shoplifting" without any significant increase in business. "I think most our business comes from right around here," she said.

Jelleff's, a chain of local women's specialty clothing stores, had a 68 percent increase in its business when the Crystal Dainery opened down the mall from its Crystal Square location, according to the store's former manager, Carol Gardell.

The combination of the Metro and the restaurant, according to Gardell and her successor as manager, Pat Ballentine, has brought an increase in business of 35 percent on Saturdays and a smaller increase in the evenings. Whereas noon hour business had accounted for 75 percent of the stores's receipts, the two women said, it now is only 60 percent of the total - so great has been the increase in Saturday and evening activity because of Metro that it overshadows the increase in lunch-time business. "The whole thing has increased, and that's the beauty of it," Gardell said.

In contrast of Jelleff's experience in Crystal City, the Silver Spring branch of the same store has found no influence on its business because of Metro, according to assistant store manager Kay Heimerling.

Silver Spring now is the northern terminal of the Red Line, which runs through northeast Washington, through the downtown business area blocks from the core of the Silver Spring is a major commercial area, the Metro stop is located several blocks from the coer of the Silver Spring area along Colesville Road.

Commuters who ride Metro to and from Silver Spring can take a bus to continue their ride without coming anywhere near the shopping area of Silver Spring.

Several merchants in Silver Spring also complained about a lack of parking, which they said makes it more difficult for shoppers. Some commuters, according to Silver Spring merchants, are parking in Silver Spring - taking up spaces formerly used by shopppers - and then taking Metro the rest of the way into Washington.

The manager of a chain of women's casual wear stores said that Metro had had "some impact" but that "business hasn't been booming, but it had brought people out from downtown." In the evening, she said, business is "dead."

The most conspicuous exception to the relative lack of impact to retail business in Silver Spring was the J.C. Penney store at 8656 Colesville Rd. The store's manager, Flora Solano, said that Metro has had a "tremendous" impact on Saturday business.

"We couldn't imagine what happened the first Saturday," Solano said. "We had a flood of people and the we realized the Metro had opened. Then we thought it was a fluke." But business on Saturdays has beer up 20 percent or so every weekend since Metro began Saturday operation, Solano said.

At the same time, however, Solano said that Metro had had "no day effect at all." To benefit from Metro, she said, stores had to be open in the evenings and on Saturday.

Metro also has proved a boon to the Twin Towers Apartments at 1110 Fidler La., about a block from the Silver Spring Metro stop. "I've rented lots of apartments to people just because we're located near the subway," Grace McCarthy, building manager, said. "Our advertisements always mention Metro. It's one of our selling points."

McCarthy said that before Metro came to Silver Spring the 360-apartments she managed had a 12 percent vacancy rate. That rate has now been cut to four percent, a reduction she attributes largely to Metro. She estimated that 60 percent of the building's residents leave cars behind and ride Metro to work.

In fact, McCarthy said, she rents about 100 parking spaces a month, at $30 each, to commuters who drive to Silver Spring, park their cars there for the day and then ride Metro into the city to work.

"This particular area where we're located is a really good area for older people who cannot drive," because of its proximity to Metro, she said. "We're renting a lot to older people."

At least one housing developer said that he believes Metro will also change community patterns. Leonard Abel, a general partner in two firms that are building town houses and apartments near Pentagon City along the Blue Line in Virginia and near Nicholson Lane along the Red Line in Maryland.

"One of the things we think is going to happen is that people who think they have to be a two-car family will find they only need one car," Abel said. "They'll find they can walk to Metro and let the wife keep the car at home."

With gasoline prices going up and Metro increasingly convenient for business, commuting and shopping. Abel said, people will change their habits. "Downtown Washington will be economically viable it won't even be funny," he said.

Raymond Kass, senior vice president of Charles E. Smith Companies, a large real estate management firm in Washington, said downtown office space is "hard to find" and "tighter than I've ever seen it" despite continuing construction of new office space.

Rentals, according to Kass, have increased from $13 a square foot to $25 and $30 a square foot for retail space in areas near Metro stops. "That's a hell of a big increase even in this business," Kass said.

Even those higher rents are drawing tenants. "It's much easier to get the rates we have to charge because - (Tnants: don't come tight out and say so - but that Metro is really beginning to have an impact."