Metro successfully inaugurated subway service to Far Northeast Washington and Prince George's County yesterday as motorists filled the huge parking lot at the New Carrollton station and turned into subway riders.

"We think things went beautifully," siad Dee Allison, transit administrator for Prince George's County, "especially considering that it was a first day."

People from Gambrills, Annapolis, Bowie, Greenbelt and Charles County descended on the 1,900-space New Carrollton parking lot just inside the Beltway and filled it by 8:45 a.m. Some motorists had to be turned away.

Big new lots at the Landover and Cheverly stations, however, were never more than half full yesterday and the Deanwood and Minnesota Avenue stations in the District of Columbia did a slow business all day.

"Parking here and going in by train, I'll get an extra hour of reading time, which is a lot better than windshield time," said Lou Kennedy of Annapolis as he parked at New Carrollton. Kennedy used to drive to the Stadium-Armory station and park.

There were the usual problems with farecard, Metro's automated fare-collecting system, and they were exacerabated by a high number of first-time Metro users. The parking lot gates and the electric signs that are supposed to tell people when the lot is full did not work at New Carrollton, but plenty of Metro employes were on hand to solve problems. The trains ran well, according to central control, and only three were taken out of service all day and only one of those three during rush hour.

The Orange Line brings Metro to 31 miles of operating subway and 33 stations and the inaugural brought out what has now become a predictable collection of riders. There were the subway buffs who never miss an opening, the joy-riders who just want to see where things go, and the people who used to take the bus.

Joan Parks, a file clerk who lives in Cheverly, used to take three buses to get to her job in Crystal City, and she had to leave the house by 5 a.m. Yesterday she didn't leave until 5:55. "A whole hour of sleep, it's wonderful," she said.

One thing that confused some riders was the fact that the new Orange Line and the old Blue Line are, for all intents and purposes, one and the same until more construction is completed. Many riders at the Minnesota Avenue and Deanwood stations asked attendants if they had to transfer to another train at Stadium-Armory. They did not.

Sherlene Duckett, of Northeast Washington, was the first person in the Deanwood parking lot yesterday. She was taking the train because "I lost my parking space at the Agriculture Department," she said.

Metro officials expect that the Orange Line will add 20,000 to 25,000 people per day to the average weekday subway ridership of about 205,000. Some of those riders wil come e after Dec. 4 when about 45 bus routes will be rearrearranged to tie in with the five new subway stations.

Two bus lines, the T17 and T19 expresses from Bowie/Crofton were tied in to the New Carrollton station yesterday and in seven morning trips they delivered 317 people to the subway system.

One of those riders, a Library of Congress employe, looked out the window of the subway as it sped toward Cheverly and pointed to the bumper-to-bumper slow-moving traffic on the parallel John Hanson Highway (U.S. 50).

"I'm always amazed at things like that," he said. "They were running test trains here all last week and everybody could see that the Metro was much faster. I was in a bus that was stuck fast for 20 minutes.This will be a little more convenient."

The farecard problems at New Carrollton were familiar and predictable. At 7 a.m., as passenger traffic through the station peaked, two of the four vending machines broke down. Metro employes sold preencoded $2 facecards. During the evening rush hour, long lines formed at the addfare machines - where passengers can add value to their existing farecards if they do not have enough to get out of the station.

However, about half of the people entering at New Carrollton had already purchased their farecards, a fact that saved Metro considerable trouble.

The big story yesterday was the parking lots. Cars were trickling into them as early as 5:30 a.m. and at 7 a.m. the new off-ramp from the Hanson Highway to the New Carrollton lot was a steady stream of automobiles.

There are three lots accessible from that side of the station. Electric counters ae supposed to tally the automobiles that cross them, then close the gates to the lots and turn on a sign on the access road that says Lot Full. Those gates and signs were not activated yesterday morning so people started circling the lots looking for parking places that were not there.

Metro employes waved them toward the few remaining spaces until they, too, were full. A blue late-model Ford pulled up then, and Metro's Thomas Forrest told him the bad news.

"Absurd," the driver said. "That's ridiculous. What awful planning."

There were some minor but irritating problems in the evening at the exit gates where parkers are supposed to pay a 50-cent fee, but for the most part the lot cleared smoothly and quickly.