When Maryland's 37,000 teachers organized two years ago to protest a cutback in their pension benefits, they printed posters attacking the man they blamed above all for the change: Senate President Melvin A. Steinberg.

But Steinberg, a Democrat and former labor lawyer from Baltimore County, not only continued to support the controversial measure, he maneuvered it through the usually fractious Senate in less than seven hours.

A few days later, he ruthlessly quelled a revolt by a group of Montgomery County senators trying to hold up funds for the Baltimore subway.

Steinberg recessed the chamber over a chorus of protests and returned later that day, votes for the subway in hand.

"You run the gavel or the gavel runs you," he said.

Today Steinberg, 52, a senator since 1967 and Senate president since 1983, made what may be the toughest stand of his legislative career: He single-handedly blocked a multimillion-dollar deal with Chase Manhattan Bank that would have relieved the state of responsibility for one of Maryland's crippled savings and loan associatons.

The deal was negotiated by Gov. Harry Hughes and supported by House Speaker Benjamin Cardin, both of whom said they were disappointed and surprised by Steinberg's decision.

Steinberg, standing alone before a bank of television cameras, a dozen reporters and at least a score of fellow lawmakers, said, "It became apparent to me that, as president of the Maryland Senate, I could not use personal persuasion in good conscience, asking these senators to vote for something that I, in my mind, was not certain was the right decision to make."

According to several lawmakers, the scene goes to the essence of Steinberg, a rotund, bespectacled legislator who is renowned for his humor yet described by many colleagues as the toughest leader the Senate has had in years.

Married and father of three children, Steinberg, who is widely known as Mickey, is a liberal and a strong supporter of abortion rights. He also has a strong independent streak: a favorite of organized labor, he has shown no reluctance to oppose his union backers when he disagrees with them.

Steinberg, who is the son of Russian-born Orthodox Jewish immigrants and grew up above the family grocery store, said he made his decision this morning after leaving synagogue, where he said his daily prayers in memory of his late mother.

As he was leaving, he said, he asked several friends, retired business leaders, what they thought of his dilemma. "They said, 'Do what you think is right,' " he said, "I said, 'That clinches it.' "

Steinberg's decision came at a time when he likely could have lined up the votes to approve the agreement, despite the reservations of a number of senators.

Many lawmakers, including Steinberg, represent districts where depositors are increasingly angry and frustrated over their inability to get at their money.

More and more, these people are vowing that in the upcoming election they will take out their displeasure on representatives who fail to deliver.

Several senators, including those who have previously clashed with Steinberg, applauded his decision as both courageous and responsive to their concerns.

Said Sen. Catherine Riley (D-Harford), "There is obviously a political liability in all this. The easy thing was just to support it and blame the governor if it didn't work."

As for Steinberg, he said he was ready to accept the consequences of his decision. "It's my act," he said.