Washington's Metro subway will take another great leap forward a week from tomorrow when the Orange Line opens between D.C. and New Carrollton and becomes the first Metro link to reach as far as the Capitol Beltway.

The new line, which will add five stations and 7.5 miles to the operating Metro system, also will bring high-speed mail service to the east side of the Anacostia River in the District of Columbia and to Prince George's County for the first time.

The New Carrollton terminal is located just inside the beltway at John Hanson Highway (Rte. 50). During rush hour when higher fares are in effect, the ride to New Carrollton will be $1 and 28 minutes from Metro Center at 11th and G streets NW.

Trains will reach speeds of 70 m.p.h. as they roll from New Carrollton to the Landover and Cheverly stations to Prince George's County and then into Northeast Washington.

After stopping at two new stations there - Deanwood and minnesota Avenue - trains will cross the Anacostia, then dive underground in the RFK Stadium-Armory station.

This new section of Orange Line is the first Metro segment to be opened that will have substantial parking available at its stations. A total of 4,000 parking spaces are located at the Orange Line stations - most of them at either New Carrollton or Landover.

The John Hanson Highway corridor is one that has been underserved by public transit, particularly when compared with such major suburban routes as Georgia Avenue in Montgomery County or Shirley Highway in Virginia.

Because of that, many transportation observers think that the New Corrollton line will provide one of the first genuine tests to see if Metro has the ability to ease pressure on the existing highway system.

It is more likely, in the view of other experts, that while Metro will carry large numbers of people, the highway will just fill up again Tremendous Washington-oriented growth is currently under way in sections of Prince George's and Anne Arundel counties that are within quick driving distances of the New Carrollton and Landover parking lots.

Metro's planners expect that New Carrollton will bring about 20,000 to 25,000 new riders a day to the subway system - approximately the same increase that resulted after the Red Line extension to Silver Spring was opened in February.

Metro has been averaging between 205,000 to 210,000 riders on weekdays in recent weeks. Saturday service has been attracting an average of 69,700 riders since it began on Sept. 30.

Metro is also planning to change about 30 bus routes that presently serve the corridor of the New Carrollton line. Buses that once came all the way into downtown Washington or to closer in Metro stations will be rerouted to connext with one or more of the five new stations.

Almost all the bus route changes will take place Dec. 3, two weeks after the subway line opens. An exception to that will be two express rush-hour routes from Bowie to Washington. Both the T17 and T19 buses will run only as far as the New Carrollton station, starting with the first day of subway service.

The New Carrollton opening will also bring with it new Metro pricing mechanisms in both parking fees and fares.

The parking fees are designed to encourage commuters to park far out, not close in. At New Carrollton, each of 1,900 spaces will cost 50 cents a day. At Cheverly and Landover, with a total of 1,500 spaces, parking will be 75 cents a day. It will cost $1 a day to park at Deanwood or Minnesota Avenue - the same price Metro charges at its lots on the Red Line. There are a total of about 550 spaces at those two stations.

The D.C. Armory Board and a private operator currently charge $1.25 for parking near the Stadium-Armory and Pentagon City stations, respectively.

Passengers who either enter or leave the subway system at the two new D.C. stations - Minnesota Avenue and Deanwood - will receive an automatic 10-cent reduction in rush-hour fares. That reducation represents a specific additional subsidy the District of Columbia government decided was warranted for the low-income residents of those Northeast neighborhoods.

Metro's rush-hour subway fares, which are charged weekdays between 6 a.m. and 9:30 a.m. and between 3 p.m. and 6:30 p.m., are based on mile-age traveled. There is a minimum charge of 40 cents for three miles plus 8.5 cents for each additional mile.

The Deanwood-Minnesota Avenue subsidy will mean that ride from Deanwood to Metro Center will cost 55 cents - a 10 cent reduction from the regular fare. The ride from nearby Cheverly to Metro Center will cost 75 cents. There is no extra subsidy there.

Metro's 50-cent flat fare for all off-peak subway trips will remain the same at both Minnesota Avenue and Deanwood, as well as throughout the system. That fare is charged during midday, after 6:30 p.m. weekdays, on holidays and all day Saturday.

The Orange Line, like the Red Line from Union Station to Silver Spring, is mostly above ground and is located primarily alongside a main railroad line - in this case the Amtrak-Conrail line from Washington to Baltimore.

A combination of topography and the necessity of putting a Metro station between two Amtrak tracks resulted in the unique design of the Cheverly station. There, the mezzanine leading to the two Metro platforms is suspended over the Amtrak rails, instead of being tunneled under those rails as has been done at several other locations.

The New Carrollton Metro station has been constructed so that Amtrak can join Metro in a joint terminal. An existing Amtrak Metroliner station is located a few hundred yards northeast of the Metro station, but Amtrak is completing plans to move to the Metro location in another two years.

The opening of the Orange Line will mean that present Metro riders will have to get used to a new symbol on their trains. Instead of boarding trains marked Stadium-Armory on a blue background, they will board trains marked New Carrollton on an orange background. Persons boarding on the Orange Line and wanting to go downtown will board trains marked National Airport on a blue background.

When planned extensions to both the Orange and Blue lines are opened, they will share the tracks between Rosslyn and Stadium Armory, but riders will have to use different trains for destination beyond those two points.

The opening of New Carrollton brings with it the opening of Metro's first on-line service yard, and that is good news for Blue Line riders. Trains can be washed and serviced at New Carrollton and will thus be washed more frequently. There are no maintenance facilities on the present Blue Line and major repairs or minor washing have required shuttling the trains to the Red Line, a time-consuming, schedule-destroying process.

The new Orange Line also means improved service on the Blue Line, because rush-hour intervals between trains will be reduced from 6 to 5 minutes. That is made possible by the improved turnaround switching at New Carrollton as opposed to the present jury-rigged operation at Stadium-Armory.

With the opening of New Carrollton, Metro will have 31 miles and 29 stations in operation. The entire system is planned to be 100 miles long with 86 stations.