After years of providing strong political and financial support to the concept of a regional rapid rail network, Maryland will get to join the District of Columbia and Virginia as a full Metro partner one week from Monday.

That is when trains will begin to carry paying passengers to Silver Spring on a 5.5-mile, four-station extension of the red line, Metro's original shuttle that now runs between Dupont Circle and Rhode Island Avenue NE through the heart of old downtown Washington.

The ceremonial opening will take place this Friday as politicians speak and bands play, first in the three new District of Columbia stations called Brookland, Fort Totten and Takoma, and then finally at the big one, downtown Silver Spring.

The new Metro line runs along one of the area's most established transportation corridors. It is the route of the Baltimore and Ohio railroad that connects Washington to the west.

The route has been a favorite of road builders, who once intended to bury it in concrete and call it the North Central Freeway. That idea is dead and the money for it has been diverted to Metro.

It will be the first long stretch of Metro that is above ground, and therefore will be the most interesting to ride. There are things to see along the line, from the two markedly different towers of the National Shrine of the Immaculate Conception, just four blocks from the Brookland station, to the distinctive but sadly faded architectural styles of the Takoma Park neighborhood that surrounds the Takoma station.

The line ends near the intersection of Colesville Road and Georgia Avenue, once considered the crossroads for one of the metropolitan area's most promising commercials and retail centers. Downtown Silver Spring never really made it, though, and business interests there are looking cautiously toward Metro to restore that promise.

For those who like to look out train windows, there will be free rides Friday, but, alas, only between Silver Spring and Brookland . You have to pay to get on the rest of the railrod, and you cannot ride the train from Brookland to Rhode Island Avenue that day.

But on the following Monday the Silver Spring line will begin to do its real work.

Metro is projecting now that the Silver Spring addition will bring the subway system another 30,000 riders a day within a month, and another 40,000 a day by the end of June. More than 140,000 people a day have been riding Metro's first 17 miles. Metro's newest total ridership projections are somewhat more modest - about 30,000 a day - than those first made 18 months ago for the system including Silver Spring.

Just as has already happened in the bus corridors that serve Metro's operating red and blue lines, there will be a revolution in the bus system that intersects or parallels the extended red line from Rhode Island Avenue to Silver Spring.

About 75 bus routes will be changed, primarily to eliminate duplicate bus and rail service and also to provide riders with easy connections between the bus and train systems. The bus changes will officially take place on Sunday. Feb. 19, but the first big day will be Tuesday, Feb. 21, when everybody returns to work from a three-day holiday weekend.

Montgomery County's own Ride-On bus system, a small bus network centered on Silver Spring, will be significantly expanded as Metrobus service is revised in that area, and will also provide easy connections with the right line. The Washington Post will carry a complete list of bus route changes for both Metrobus and Ride-On next Sunday.

All of the new Metro stations have at least nine bays for unloading and loading bus patrons. Regular Metrobus users who have not experienced the transfer between subway and bus will find the fare and transfer complexities confusing. Especially in the case of D.C. residents, public transit will be more expensive.

D.C. residents will have to pay a total of three fares for a round-trip involving both bus and rail on each leg: twice for the rail and once for the bus. That means an effective increase of at least 40 cents, unless they choose to stay with the bus, as many have done on other subway legs.

Maryland residents will find that, for the most part, their round-trip cost is about the same. That is because they pay a higher bus far than D.C. residents to ride into the District, but get a free bus ride back when they transfer from the train.

The basic subway fare, collected from a magnetically encoded card, is 40 cents for three miles at all times. Beyond three miles, there is a higher rate per miles during rush hours, defined as 6 a.m. to 9:30 a.m. and 3 p.m. to 6:30 p.m., than there is the rest of the time. For example, the subway from Silver Spring to Metro Center will cost 75 cents during rush hour, and 55 cents the rest of the time.

Just as is true on the operating Metro system today, it will not be possible to transfer from the bus to the train. A separate full far must be paid. It will be possible to transfer free from the train to Metrobus in either the District or Maryland, provided the rider gets his transfer from the machine in the Metro station where he boards the train. There is no transfer between the subway and the Ride-On bus. Separate fares must always be paid.

The extended red line will operate, as Metro does today, on weekdays only between 6 a.m. and 8 p.m., with no service on federal holidays. There is a proposal pending before area jurisdictions to expand weekday subway service to 11 p.m. and to provide 14 hours of operation on Saturdays, beginning in September. A decision on that proposal will be reached soon.

Tomorrow, The Post begins a series of four articles about the communities surrounding the new Metro stations Silver Spring, Takoma, Fort Totten and Brookland.