Metro's subway, steadily increasing in popularity and reliability since it expanded into Virginia last July, will start carrying riders to and from Maryland Monday morning with the extension of the red line to Silver Spring.

The opening of the new 5.5 mile segment through Northeast Washington into Montgomery County will make it possible to ride directly from Dupont Circle to downtown Silver Spring on the subway, and with a single transfer, from National Airport to Silver Spring.

Four new stations will be added, and Metro predicts, as many as 40,000 riders a day by the end of June. About 140,000 people a day are already riding Metro (the one-day record was 150,372 on Jan. 27).

Major changes in bus routes in the area of the new stations will follow in two weeks. In the meantime, there will be shuttle buses from the current bus terminal in Silver Spring to the new Metro station there.

In the eight years since construction began in 1969, Metro has been plagued with political intrigue, labor strikes and financial crises. Despite those and other problems, the opening of the Silver Spring line means that 23 miles - almost one fourth of Metro's planned 100 miles - will be in operation.

For the first time, all three of the metro Compact signatories - Maryland, Virginia and the District of Columbia - will have a piece of the action.

But the landmark addition of Maryland to the system comes at a time when Metro's future is being hotly debated in both local and federal circles and the definitions of success depend on one's point of view.

In terms of popularity with his riders, Metro is a success. Four out of five of them interviewed by The Washington Post during a recent survey said they preferred the subway to other transportation, and more than one-third said they would be taking a car or a taxi for that trip if there were no subway.

Riders from every Washington-area jurisdiction are using the subway and 15 per cent of those interviewed drove to a subway station before taking the train.

The Metrobus system has been completely realigned in the downtown region because the train provides quicker, better service. The incredible bus jams on K Street NW and 14th Street NW that used to be a regular part of the morning and evening rush hours have largely disappeared.

It is an axiom of the bus business that in bad weather, ridership will go down. Just the opposite happened to the subway during the recent storms. Metro's record week of ridership, ending Jan. 27, occurred during wind, rain, snow, sleet and misery.

One of the dreams of Metro planners was that it would revitalize downtown Washington. Woodward & Lothrop recently started a $6 million renovation of its downtown flagship store, where one-fourth of the customers come directly from the Metro Center station. Sales have increased 40 per cent in a department that was moved from an upper floor to the basement right next to the Metro exit, a Woodies official said.

Restaurants from Rosslyn to Capitol Hill have standing-room, lunch-hour crowds when a table used to be easy to get. But cafeterias in government offices close to Metro stations report their business is down.

"What rail transit needs is a success," Transportation Secretary Brock Adams has been saying recently. That is because the two newest rail transit systems in the country - Metro and San Francisco's Bay Area Rapid Transit (BART) - have been perceived as something else.

"I have no doubt that BART and Metro will be valuable," Richard S. Page said in a December interview. "But it would be nice if that perceived value could occur soon." Page is the administrator of the Urban Mass Transportation Administration (UMTA) and one of Adams key lieutenants. To Page has fallen the job of working out the federal role in Metro's future.

"By success," Page said, "we mean one of these new systems coming in closer to budget, closer to schedule, operating somoothly sooner . . . The technology is there to do these things more simply and reliably."

Metro's statistics are well known. If construction had proceeded on scheduled without congressional interference, inflation and strikes, most of Metro's 100 miles would be completed now. Instead, only 60 miles are financed. Four more miles have federal approval. The remaining 36 miles are the subject of significant federal-local debate.

Metro was supposed to operate on a break-even basis and provide enough money to pay the interest on $1 billion in revenue bonds sold to finance construction. Instead, the subway system's projected operating deficit for fiscal 1979 - begining July 1 - is $32.6 million and that does not include money for retiring the bonds. The buses that feed the subway are projected to run 62 million deficit. Most of the total bus-rail deficit is picked up by increasingly unhappy local property taxpayers.

Metro was supposed to be constructed for a total of about $2.5 billion (in 1969). Instead, completion of the 100-mile system is estimated to cost $5.1 billion to $5.8 billion, depending on whether Metro or the federal government is doing the estimating. Brock Adams keep calling Metro an $8 billion system, a figure he reaches by adding 30 years of interest on the revenue bonds to the construction cost estimate.

These are testy times for federal-local relationships on Metro. Carlton Sickles, a former Maryland congressman, longtime member of the Metro board, and one of those present at the creation of the Metro system, told Page during an emotional speech recently:

"We were encouraged by the federal government to do this from the beginning. We said we can't do this alone. The whole community is expecting to have a 100-mile Metro system." Cuts in that system he said, would be "a crime, a sacrilege."

Page, echoing Adams public position, responded by saying, "I am not committed to cutting back the system, but we want to know what happens next."

Despite the oratory, however, there is progress to report. A regional task force studying the rest of Metro has completed a major protion of its work and is preparing a report for the federal government.

Even local officials who disagree violently with the federal position call Page a reasonable, agreeable man, who has shown a willingness to bargain and listen. He operated the Seattle bus system before coming to Washington and thus became the first administrator in UMTA's history who actually has first-hand experience in running public transportation.

he has taken two steps in the past weeks to reduce the paperwork and bureaucratic burden involved in day-to-day UMTA-Metro transactions. "UMTA has nitpicked and delayed and waffled," Page said in a speech. "We are stopping."

Joseph S. Wholey, the new Metro board chairman, has promised Page that a financial plan for construction, operations and service on the revenue bonds will be in place by Aug. 31 - as not only the federal government but many area local governments are demanding.

Wholey announced last week he will not seek re-election to the Arlington County board, his local base. But he will finish most of his one-year term as Metro board chairman. He said Thursday he is absolutely committed to producing the Metro financial plan before he leaves.

Wholey's tract record suggests he will succeed if anyone can. He literally terrfies some of Metro's financial people with his grasp of the intricacies of the budget and he has successfully and openly negotiated important Northern Virginia transportation questions.

When Metro opened the blue line from National Airport to Stadium-Armory in July, there were almost three months of mechanical uncertainty before the subway system settled down.

Doors would stick open and brakes would lock. On one occasion a six-car train pulled into the Potomac Avenue station and a two-car train left, leaving the other four cars behind.

Breakdowns still happen, D.C. Council Member Jerry Moore told the Metro board Thursday about a scene reminiscent of the opening of the classis comic film, "Mr Hulot's Holiday:"

Passengers stand on platform for National Airport. Train for airport comes in on opposite track. Passengers run up escalators and down escalators, but get to opposite track too late. Train leaves without them. Passengers wait, assuming next train for airport will be on opposite track. Not so. Next train is on right track. Passengers scamper back Too late. Passengers spot Jerry Moore, recognize him as D.C. City Council member, vigorously lodge complaint

"Couldn't we have some announcements in the stations when that happens?" Moore asked Metro General Manager Theodore Lutz plaintively. "yes," Lutz said.

Despite incidents like that, Metro's reliability is better than it was and the numbers prove it. During January, 98 percent of the scheduled trips on both the red and blue lines were completed. The blue line scored about 75 percent in August.

The operation of the expanded red line will require Metro to put 174 cars into operation. It takes 13 eight-car trains to maintain six-minute rush-hour intervals between trains that Metro uses on the blue line.