Sen. Ed Thomas drove to the Maryland General Assembly session last week from his Pennsylvania-border district, armed with a folder of newspaper clippings about traffic deaths on the rutted, two-lane portions of U.S. 15 -- which he calls "Killer Road."

He has mailed many of those clippings to Gov. Harry Hughes, needling him about his unfulfilled promise to widen the highway. "Dear Harry, Chalk up two more," he penned on a recent clipping about two U.S. 15 fatalities.

Similarly, Sen. Frederick C. Malkus drove here from his Eastern Shore district last week, angrier than ever about the precarious state of the Choptank River Bridge in his hometown of Cambridge.

From Southern Maryland came Sen. James Simpson, growling about the narrow roads that spawn traffic "logjams" in the outer suburbs that reach into his still-rural district.

Even though these three men hail from districts as different as the mountains and the seashore, this year they have found something to unite them: Maryland's transportation policy, which has placed increasing emphasis on mass transit construction at a time when many state highways have fallen into disrepair.

The union of the trio, and many of their fellow rural legislators, represents the 1981 version of the age-old political struggle between the urban and rural regions of this diverse state. It pits the rural legislators against an old enemy -- Baltimore City, the citadel of Maryland political power, where the state is now helping build an expensive, eight-mile-long subway line.

In earlier days, when Maryland's rural counties dominated the state, transportation dollars poured into rural highways and bay bridges. Now 40 cents of every dollar raised through taxes on highway users goes toward mass transit systems in Baltimore or the Washington suburbs, these legislators point out with regularity.

"A lot of us are fed up to here with Baltimore City coming in here every year with an empty wheelbarrow and going home with it full," said Thomas, who comes from Frederick. "I call the people from Baltimore and Washington the Beltway Bullies. In my opinion, those subways are a cancer that is going to break this state."

Thomas, Malkus, Simpson and their rural brethren do not really expect to change the transportation equation this year. For one thing, the numbers are clearly stacked against them.

"We simple country folk aren't so ignorant that we can't count," said Del. Bill Horne (D-Talbot County), who represents part of Malkus' district in the House. "When you add up the delegations from the Baltimore and Washington areas, that's 27 of the 47 districts. That means the game is up."

Nonetheless, Maryland's rural legislators claim to be more united this year than at any time since 1976, when they filibustered for 10 days in a spirited, but losing, battle to block construction of the Baltimore subway.

They have put a cluster of anti-Baltimore bills into the hopper -- such as one to repeal the General Assembly's 1980 committment to a bond issue to renovate Baltimore's Memorial Stadium. Sen. Edward J. Mason (R-Allegany County) and several other rural legislators are talking about a bill to get the state out of the subway business altogether by creating regional subway taxing authorities in the Washington and Baltimore area.

And last week, they were busily building coalitions with legislators who have ties to the trucking industry in hopes of blocking a move for a new highway-user tax -- this one on trucks -- or at least tying it to a formula that will guarantee new funds for roads in their districts.

"We may not get what we want, but we just try to wear 'em down," said Simpson. "Sometimes it just amounts to raising hell. It may be Memorial Stadium one week, police aid the next week. But sometimes we can get them to change things a little."

The rural legislators have already gained the attention of a Baltimore City delegation, some of whose members are alarmed at the specter of an urban-rural clash.

"The last thing we need is a holy war," said Del. Frank Robey (D-Baltimore City). "I'm convinced that if it becomes a battle between Baltimore City and the rest of the state, it could cause severely difficult times for all of us. It could really hurt this session, which I believe is going to be the most important one, from a fiscal standpoint, that I've ever been involved in."

"We're going to have a lot of factionalism unless we can come up with a source of money for roads," agreed Senate Majority Leader Rosalie Abrams (D-Baltimore City). "It's going to hang like a pall over the session."

Ironically, the rural charge on the transportation issue has found some allies in Baltimore and the Washington suburbs, where legislators like Robey are also deeply concerned about the long-term health of the state's transportation trust fund, but for different reasons.

The fund finances all state transportation projects -- highways, mass transit, the Port of Baltimore, Baltimore-Washington International Airport and some rail lines -- and has suffered badly during the energy crisis, because of its heavy dependence on gas tax revenues.

As a result, legislative leaders say they plan to appoint a committee of rural and urban legislators to scrutinize the Department of Transportation, its finances and its priorities, a move similiar to one that pro-highway Virginia legislators have undertaken.

Several urban Maryland legislators say they see the committee as one way of trying to resolve the rural-urban split before it spills over into other issues.

The snow-haired Malkus, who has represented the Eastern Shore for 33 years and remembers the days when the rural interests ran the Senate, says he is not likely to put down his guns this time without a noisy fight.

"I'm going to talk more than I have in the past," vowed Malkus, one of the leaders of the 1976 subway filibuster. "Back when we ran the legislature, we were a lot kinder to them than they are to us."