For much of the Maryland General Assembly's annual 90-day sessions, the 13 members of the Senate Budget and Taxation Committee burrow into the state's $7 billion budget in relative solitude, attended only by bureaucrats, legislative analysts and an occasional reporter.

Then there are the times when B&T stages one of its patented performances, turning the hearing room in the James Senate Office Building into the best little theater in Annapolis.

More often than not, those times occur when Baltimore Mayor William D. Schaefer is in town to root around for money for his beloved and hard-pressed city.

Today, Schaefer and his antagonists on the committee put on another boffo show for yet another standing-room-only crowd.

Schaefer came before B&T today to appeal for an extra $2.9 million in state aid to Baltimore's police department, a modest enough figure by many standards, but a matter of civic life and death, according to the mayor.

"This is my first appearance before B&T this year," began Schaefer as he sat down at the witness table just a few feet from his perennial bete noire, state Sen. John C. Coolahan (D-Baltimore County). "I really look forward to it -- if I can keep my blood pressure under control."

"We'll do our best," shot back Coolahan, a devilish grin spreading across his face.

The mayor recited his usual grim statistics about Baltimore: highest tax rate in the state, home to most of Maryland's poor, beset by crime.

"Dealing with you and your administration is like dealing with the Russians," countered Coolahan. "Your figures are never verifiable."

"I can assure you now my blood pressure is mounting," said Schaefer.

The issue of police aid, based on a complex formula involving population density and wealth, has driven the mayor's blood pressure up periodically for years. The city has constantly sought adjustments as its population declined and its wealth increased.

Last year, the city wanted to extend a special two-year provision that guaranteed all jurisdictions no less aid than they received during fiscal 1982. Schaefer lost that issue and $1.2 million when a Montgomery County state senator, Stewart Bainum Jr., joined the six hard-core conservatives on B&T in killing it.

Montgomery County argues that Baltimore gets nearly half of the roughly $74 million in police aid while recording only about 30 percent of state crime. On a per capita basis, Baltimore gets $45 in police aid compared to Montgomery's $12, and the state average of $17.

But this year, the political winds could make a difference. Two of the seven members of B&T who opposed Schaefer last year -- Bainum and Catherine I. Riley (D-Harford) -- have been mentioned as possible running mates for the mayor if he seeks the governorship in 1986.

Bainum was hedging his bets today, refusing to say how he will vote on police aid: "It depends on what else is on the table." He wants the vote delayed until his county can come up with a trade-off.

Schaefer, meanwhile, was being reminded by committee members that he sometimes can be his own worst enemy.

"Mayor," said Sen. Charles H. Smelser (D-Carroll County), "let a country boy give you, a city boy, some advice: Next time you come down, let the [police] chief speak first."

"I will not bother you with my testimony on issues. I'll heed your advice," replied a seething Schaefer. With that, he scooped up his papers and stalked from the room.