Maryland's plans to eliminate eight of the state's 12 popular commuter trains was unanimously criticized by congressman, local officials and several hundred residents last week as what one called "a throwback" to the "pro-auto" days of the 1950s.

The proposed cuts in rail service are designed to save money for the state's hard-pressed Department of Transportation, which subsidizes the trains. They would eliminate next summer the three Baltimore-Washington commuter trains in late 1982, would end all five commuter trains that make round trips on weekdays between Brunswick, in Frederick County, and Washington by way of Rockville.

The proposal would virtually end all rail service along the Brunswick line for more than 4,000 commuters. Amtrak, in a separate action, next summer plans to eliminate the Blue Ridge, one of two interstate trains that now make daily round trips along the same line, carrying 500 commuters.

State officials said the cuts in the Baltimore-Washington corridor could come as early as next July for the two Conrail trains that carry about 1,000 commuters on daily round trips between Balimore and Washington. The state would also end its support of Amtrak's long-haul commuter train, the Chesapeake, which makes a round trip daily between Philadelphia and Washington.

The trains will stop running because the cars are on loan from New Jersey, which will need them back by next fall. State support will continue for four B&O commuter trains that now operate daily round trips between Baltimore and Washington.

Maryland does not have enough money to buy new passenger cars, which can cost as much as $1 million each. State officials said no more used cars are available in this country. Maryland has been trying for more than a year to buy 20 cars from Connecticut, which that state has not decided to sell.

Ridership on the B&O Brunswick line has increased dramatically, by more than 35 percent in the last year alone, and had doubled on the Conrail trains since 1972. Most of the commuter trains already have standing room only.

Although the Department of Transportation plans to study the impact of its proposed cutbacks, they are expected to stand unless the governor or the General Assembly acts to provide funds for the commuter rail program.

At a hearing on the 1980 State Rail Plan last week at Glen Burnie, Sen. Paul Sarbanes (D-Md.) strongly criticized the plan, saying the state should be working "to maintain and improve rail service," not curtail it.

Commuting from Baltimore to Washington by train now costs less than $2 each way, on a monthly ticket, compared with more than $7 each way on Amtrak. Commuter tickets on either Conrail or the B&O trains can now also be used on Amtrak trains, but Amtrak has announced it will end that practice next year.

State officials contend that the eight round-trip commuter trains it plans to eliminate offer "duplicative" service. The Brunswick B&O line will be in the same "service area" as the Metro subway when it reaches to Gaithersburg in 1983, state officials say, and the Conrail commuter trains parallel the four state-subsidized B&O trains.

But such Anne Arundel County residents as Frank Karwoski, one of hundreds of daily Conrail commuters to Washington who board at Odenton near Baltimore, argued that the B&O and Conrail lines are "miles apart and serve different communities. I would have to drive 15 miles to Laurel, though stop-and-go traffic, or drive 10 to 15 miles to the New Carrollton Metro subway station where there is no parking."

One Baltimore resident, Sylvia Schildt, who works in the advertising department at Woodward and Lothrop in the District, said, "That's the end of my job (if they drop the Conrail trains). I need the flexibility of a number of trains, of knowing I won't be stranded if I miss one."

At the Rockville hearing, Ross Capon, executive director of the 11,000-member National Association of Railroad Passengers, said Metro and the Brunswick line were "no more duplicative than I-95 and the Baltimore-Washington Parkway."

Like all forms of mass transit, the state's commuter rail program loses money. The state subsidy now is about $1.7 million a year, half of the $3.5 million B&O and Conrail lose on the routes. Federal programs pay the other half. Maryland also subsidizes rail freight in the state, and plans to continue those supports.

Most state transportation funds come from the 9-cents-a-gallon gasoline tax, which has provided dwindling revenues because motorists are driving less. Gov. Harry Hughes had proposed raising the tax -- last increased in 1972 -- but recently said he had changed his mind.

The state is expected to announce other transportation cutbacks next week.