Traffic officials in the District of Columbia are counting on mass transit, and especially the region's new Metro subway system, to move thousands of visitors and spectators in and out of downtown Washington on Tuesday, Inauguration Day.

Barring mechanical problems, Metro officials believe trains should be able to move all the passengers who want to ride on Tuesday. But the day's operations could provide an acid test of the subway's cranky Farecard system, which requires each passenger to buy a magnetic ticket to enter and leave station turnstiles.

Parking of private cars at curbside in a large part of downtown Washington will be severaly restricted from 12:01 a.m. until 11:59 p.m. Tuesday. The prohibited zone, to be marked by special "emergency -- no parking" signs, will extend generally from Rock Creek Park on the west to the Library of Congress on the east, and from K Street on the north to Independence Avenue on the south.

At 10 a.m. Tuesday, police will barricade a somewhat smaller area around the Mall and the inaugural parade route to all automobile traffic. With limited exceptions, bus service also will kept out of the area.

The auto-free zone will extend generally from the Lincoln Memorial on the west to the Library of Congress on the east and from Independence Avenue on the south to a block or two above Pennsylvania Avenue on the north. Regular traffic will be resumed about an hour after the inaugural parade ends, about 4 p.m.

The Southwest-Southeast Freeway, the Center Leg Freeway (I-395) beneath the Mall at the foot of Capitol Hill and 23rd Street NW will be kept open. Independence Avenue will be kept open except for a brief period before and after the presidential oath-taking, when a section near Capitol Hill will be blocked. Sections of Constitution Avenue will be kept open, city traffic officials said, but may be closed when police judge it necessary.

On Monday, public parking on the Mall between 7th and 14th streets will be prohibited after 10 a.m. because of Vice President-elect George Bush's reception at the National Museum of American History.

Regular offpeak fares will be charged on subway and bus lines Tuesday. Except for senior citizens who ride at a reduced fare this means everyone taking the subway must have a Farecard worth at least 60 cents in ech direction.

This contrasts with Jimmy Carter's inaugural four years ago, when the then-much-shorter subway was free part of the day and a 50-cent fare was collected the rest of the time by the primitive but fail-safe method of tossing coins in a barrel. The fare-free service in 1977 was subsidized by a $4,000 payment from the Carter Inaugural Committee.

Hoping to avert lines of angry passengers at stations on Tuesday, Metro General Manager Richard S. Page urged would-be riders to buy Farecards before that day -- and to remember that each member of a family or riding group must have a card. A card valued at $2.40 will not, for example, let four people through the gate.

Metro has recruited 41 administrative employes to sell precoded $1 Farecards at strategic stations where long vending machine lines are expected. fThese will permit one person to ride one way, with 40 cents remaining value that can be traded in or otherwise used for later travel -- including use of the Addfare machine on the return trip.

The Metro subway system, which has grown since 1977 from 5.7 miles to 37 miles, will be operated Tuesday from 6:30 a.m. to midnight. Six-car trains will run every 12 minutes on each outer branch of the Orange and Blue lines -- every six minutes common inner trunk -- and trains will run every 10 minutes on the Red line.

The Metrobus syste will be operated on a basic Saturday schedule, which omits morning and evening rush hour service to employment centers, where many employes will be given the day as a holiday.

On 50 bus routes, however, extra midday and late afternoon service will be operated to carry spectators at inaugural events to and from subway stations or to downtown. (A list of routes with supplemental service appears on B2.) Offpeak fares will be charged -- a basic 60 cents, plus a surcharge for crossing from Maryland or Virginia into the District.

Free fringe parking will be provided for Virginians at the north parking lot of the Pentagon, with free shuttle bus service to and from the Arlington Cemetery subway station. Regular fare will be charged for the train rides. The shuttle bus service will continue into evening until the parking lot is substantially emptied, according to James Rouse, Metro bus operations superintendent.

Fringe parking for a fee will be available for Metro subway patrons at several stations in Maryland and the District, notably Silver Spring, Fort Totten, New Carrollton, Addison Road and Rhode Island Avenue. In most instances, a $1.25 charge will be collected.

A concessionaire for the D.C. Armory Board will open lots at the Stadium-Armory station for inaugural spectators for a curiously inverted tariff -- $1.25 for those who arise before noon and park all day, $2 for those who arrive later and park half a day. Asked to explain, the woman who answered the phone at the armory general manager's office replied. "It's their policy."

For passengers going to the swearing-in ceremony at the West Front of the Capitol, the most convenient subway stations are Union Station and the east exit of the Judiciary Square station on the Red Line and the Capitol South and Federal Center Southwest stations on the Blue/Orange Line.

For those going to or leaving the parade, the most convenient stations are Metro Center on both routes, Judiciary Square and Gallery Place on the Red Line and McPherson Square and Federal Triangle on the Blue/Orange Line.

Metro officials warned passengers that the north entry of the Smithsonian station in the middle of the Mall will be closed until at least 6 p.m. on Inaugural day, so parade spectators should not plan to use it.