The theme of the 1980 Maryland General Assembly session opening here today may have been foreshadowed one afternoon last March when the state Senate refused to give Baltimore a few million more dollars in police aid.

Although the issue itself seemed incidental, the fury and embarrassment with which Baltimore's senators reacted to the vote signaled that more than the money was at stake. Several suburban Washington legislators voted against Baltimore that day, and in so ding chiseled the first crack in an alliance that had dominated the legislature for a decade.

For the next 90 days, as the legislature deals with issues ranging from mass transit funding to money for Baltimore's stadium, the political alliance between the two metropolises will be tested as never before.

"The coalition's on tenuous ground; even more so than in the past few years," said Sen. Peter Bozick, former chairman of Prince George's eight-member Senate delegation.

Bozick, whose political mentor, former Senate President Steny Hoyer, championed the coalition and held it together for most of the last decade now says: "I'm sick and tired of saying 'Let's help Baltimore.' They're looking for school aid, for money for a stadium. I say -- enough."

Bozick's is certainly not the only view.

His Hyattsville colleague in the Senate, John J. Garrity, who agrees that Baltimore "was just too greedy last session," believes the coalition will hold. "We are going to see cooperation this year. We have mutual beneficial programs that will need mutual support."

On the mass-transit issue in particular, there is general agreement among the lawmakers of Baltimore and suburban Washington that they must hang together if their plans are to survive the traditionally virulent opposition of the state's rural legislators. But voting together will mean reconciling their often divergent views on where the money will come from and how it will be parceled out.

The legislature was unable to agree on a solution to the funding questions last year, and suburban Washington legislators came home blaming Baltimore and the legislative leadership for the make-shift, one-time grant to Metro that eventually passed.

This year, as the Washington suburbs face a federal deadline for finding a permanent source of operating money, the bargaining will begin with the controversial and still tentative recommendations of a transportation task force that emerged from last year's debate.

The task force recommended that money for construction of new roads and the Baltimore and Washington subway ststems be raised, in part, by an increase in the state gasoline tax, and that the state pay three-fourths of the local operating costs of the two systems. The rest of the money could be raised, the commission said, by sales tax increases in Baltimore and the Washington suburbs.

Both the Baltimore and suburban delegations strongly oppose part or all of that plan. But so far, they are not close to an agreement on how to change it.

Baltimore's legislators say thay oppose the tax increases, and are reluctant to agree to any proposal that would require the city to pay the operating costs of its system, which currently are funded completely with state dollars.

Many prince George's and Montgomery legislators also oppose tax increases, but their favorite alternative -- dedicating part of the current sales tax to transportation needs -- was opposed last year by the Baltimore-dominated leadership and Gov. Harry Hughes.

Both sides are predicting a solution this year, but no one can say how it will happen.

"It would be an abject failure of leadership if we didn't work out a stable source of Metro fundings," observed Del. Luiz Simmons (R-Montgomery). "We will work something out -- the only question is how far are the local counties going to have to go to do it."

In the opinion of many members of Prince George's delegation, other fiscal matters, including Baltimore City's pet projects, may go nowhere until the transportation issue is acceptably resolved.

"We're bound and determined to keep Metro funding in the forefront so we don't get sloughed off like last year," said Del. Robert Redding, the chairman of the Prince George's delegation. "We need to assert ourselves more with Baltimore City and demand that we get support for our needs, just as they do."

For Baltimore legislators, there are issues this year that carry equal weight with transportation funding, including passage of a new package of state aid to education, and funds for the renovation of Memorial Stadium, the city's museums and libraries, and the port of Baltimore.

And in the middle of all the funding disputes sits a projected state budget surplus of $229 million, eyed greedily by all legislative factions.

"There'll be a billion-and-a-half dollars worth of requests for that $229 million before we're through," predicted Sen. Arthur H. Helton Jr. (D-Harford).

While proposals have already surfaced to use part of the surplus for the transportation and education funding packages, other ideas abound for returning it in the form of tax cuts or preventing its reappearance in future years with spending limits and other reforms.

The fate of these measures could be inextricably linked to the strength of the Baltimore-Washington alliance.

Time and again in the past, the regions have joined together on economic issues important to them. The payoffs have been substantial. Together they assured passage of Washington Metro financing in the early 1970s, construction of the Baltimore subway, a one-time redistribution of amusement taxes that provided a windfall for Prince George's, and building of the Baltimore convention center.

But through it all the legislators from the two regions have not grown exactly fond of one another.

"Baltimore, as you probably know, loves to get its hands on as many dollars as it can," says Sen. Laurence Levitan (D-Montgomery), as he begins a conversation about the issues facing the legislature.

"Those guys from P.G. want to get everything out of the state they can this year. They don't care who they hurt," parries a Baltimore legislative leader, who asked to remain nameless.

Responded Prince George's Del. Timothy Maloney: "I don't go along with any deal for Baltimore until we see what we get on Metro. That's going to be the stock answer this year."

"After years of being outtraded and outmaneuvered by them, we've given away everything but our socks," says Sen. Howard Denis (R-Montgomery) of his colleagues from Baltimore.

And Del. Paul Weisengoff, a powerful Baltimore Democrat who is not above using less than subtle techniques of persuasion, opines: "Those Washington legislators read so much about the wheeling and dealing, they say 'We're going to do it, too.' But if they try and tie up the legislature on Metro they are only going to antagonize a lot of people."

Even if the legislators from the two metropolises can compromise their views on transit funding, they still could face a real threat from rural and conservative legislators, who say they are fed up with their road programs being obliterated by mass transmit needs.

Every mass transit push in the past decade has met with a filibuster in the state Senate, and it takes 32 votes -- more than the Baltimore-Washington coalition alone can muster -- to break one.

The only way they were broken in the past, according to Sen. Thomas V. (Mike) Miller (D-Prince George's), was "with the guiding hand of Gov. Marvin Mandel," who could always pull out a few votes when they were needed.

"But now things are very different," said Miller. "We don't have a strong leader at the top. There will be door-slamming and name-calling," he predicted. "It's going to be a difficult year."