The New Carrollton Metro Station has its own brand new off-ramp from U.S. Rte. 50 just inside the Capital Beltway, four magnificent new parking lots containing a total of 1,900 spaces, and enormous potentials for becoming the site of a major traffic jam.

"We're having this little nightmare," said Dee Allison, Prince George's County transit administrator. "The lot farthest from the road fills up first, but people can't see that it's full. Once they get inside, they can't get out unless they pay 50 cents. So they back out the entrance lane and everybody is stopped cold."

To deal with that "worst-case situation," as the engineers would call it, the county has installed electronic signs telling motorists when the various lots are full and is planning to have lots of county employes directing traffic when the New Carrollton lots open Monday morning along with the Metro Orange Line.

The Orange Line is bringing with it almost 4,000 parking spaces at the five new Metro stations. Almost all of those spaces - 3,400 - are in Prince george's County at the New Carrollton. Landover and Cheverly stations.

The county has done what is far and away the best job in the metropolitan area of hanging signs out on the roads so people can find their way into the Metro stations and the station parking lots.

Both the new Carrollton and Landover stations are readily accessible from either direction of U.S. Rte. 50. The Cheverly station, however, can be reached only from U.S. Rte. 50 east-bound - outbound - and has exits only to U.S. Rte. 50 westbound - inbound. Access is also possible from local roads around the station. The Cheverly station has only 500 parking spaces.

The New Carrollton Station has three lots accessible from U.S. Rte. 50 or the Beltway and one lot on the north side of the station accessible from Maryland Rte. 450 by way of Harking Road, a new street. It is not possible to drive directly from the Harkins Road lot to the three lots served by U.S. Rte. 50.

The U.S. Rte. 50 exit ramp also serves the Amtrak Beltway station. About two years from now, that station will be moved to a new location immediately adjacent to the present Metro station. It is possible that as many as 600 more parking spaces could be added then, but the county is balking at picking up half the cost of a new parking facility. The other half would be paid by the Federal Railway Administration under its Northeast Corridor improvement project. With the money would come some complicated federal strings. Negotiations are still under way.

Parking fees at all of the stations will be paid to machines at the exit points. The machines at the exit points. The machines are similar to exact-change lane machines one encounters on turnpikes or just before entering the Baltimore Harbor tunnel. Exact change is required.

Metro is going to charge 50 cents for all-day parking at New Carrollton and 75 cents for all-day parking at Landover and Cheverly. Parking at other Metro-owned lots - including those at the new Deanwood and Minnestoa Avenue stations - will cost $1.

The purpose of this parking policy is to encourage people to park on the fringe of the urbanized core rather than to drive into it.

Extra protection by both Metro and Prince George's County police is planned at all the station parking lots.

"We are certain that there are going to be problems we just haven't thought of yet," Allison said. "We'll try to solve them as quickly as we can."