For commuters inaugurating the Stadium-Armory Metro stop, today, their voyage will begin not at the station's gleaming entrance, but two blocks away on the Plains of Asphalt, a 1,000-car parking lot.

The commuter must skirt a sea of parked cars, cross East Capitol Street's rush-hour traffic, risk being stranded on "Tear-Drop" island, and finally brave a rickety wooden walkway that spans a moat of dirt, mud and unfinished road.

If the lights are favorable, the trip from the middle of parking Lot No. 3 on East Capitol to the Metro stop entrance takes five minutes.

The Stadium Armory stop is one of the most difficult to reach of Metro's 17 stations opening today, but it is not the only one with access problems. The Pentagon City station sits amid a desolate field, and the Rosslyn station area in some places has no sidewalks at all.

Those who arrive early enough at the Stadium-Armory station can squeeze into the 240-car lot on 19th Street between Independence Avenue and East Capitol Street, a one-minute walk from their cars to the escalator taking them to the train.

But the 240-car facility "will be full all the time," said Bob Allen, resident engineer for Metro at the site.

The spillover will have to go to the gigantic East Capitol parking lot across the street from the Armory. The spillover from this lot will park as far as a half mile away in the 12,000 space lot serving the Robert F. Kennedy Stadium. The cost is $1 a day for all the lots.

Metro is directing people to cross East Capitol at 19th Street, Allen said. "Somebody's going to get hurt if they try to cross anywhere besides East Capitol and 19th Street," Allen said.

The traffic light on the southeast corner of East Capitol and 19th Street allows pedestrians 33 seconds to cross the 80 foot street.

Those caught midstream by the changing light will have to crowd onto the 12 by 3 foot concrete-tipped portion of the median strip or stand in the median's crab grass, which is littered with broken bottles and cigarette butts.

There are no plans to enlarge the paved area of the median, but transportation officials say they will keep a close eye on the intersection and lengthen the traffic light's cycle if pedestrians have inadequate time to cross the street.

"For a while things are going to be a little chaotic, no question about it," said Paul Wolf, a traffic engineer for the District Transportation Department.

Wolf said he has ordered a pedestrian signal for the crossing but that it will probably be a month before it will be installed. In the meantime, a simple red-yellow-green traffic light will suffice, he said.

The Pentagon City station across from the Western Electric Plant on Hayes Street in Arlington rises above a moonscape of flattened earth and mounds of dirt.

Arlington transportation officials, in an 11th-hour effort, completed an asphalt sidewalk leading from the station's platform south along Hayes Stree and west along 15th Street.

North of the station is nothing but a barren tract of dry earth. Tenants of the more than 1,200 apartment units whose rooflines can be seen above the dense underbrush and the dense underbrush and scrub trees that separate them from the station must walk a quarter mile to reach the Metro entrance.

If they take the northern route along Army Navy Drive they must either walk along the busy roadside or at the edge of fields waist-high with Queen Anne's lace. There are no sidewalks north of the station.

Rosslyn's $42 million Metro station offers no terminal for the 80 buses a day that will come to the end of the line in front of the station.

For the commuters, there is no sidewalk, only a pile of dirt, a vacant lot, and N. Moore Street, which, already provides a serious challenge to pedestrians who would venture across its often congested four lanes.

Sidewalks and easy acess to the surrounding buildings won't be available from the Metro station until a planned office building is completed sometime in 1980.