The debate on the measure to cut Maryland's sales tax by a penny was supposed to be routine. Republicans and conservative Democrats would get their chance to talk about wasteful government spending and unnecessary taxes. Then the Senate would agree quietly with a committee decision to kill the cutback proposal.

That's the way it was supposed to work out. But then Montgomery County's senators got mad.

Two hours before that debate was to begin, Montgomery legislators were told that their county would lose $9.3 million if a separate package of tax relief legislation supported by House and Senate leaders actually became law.

Furious that they had never been fully consulted on the impact of the tax relief legislation, the four Montgomery County senators decided that they would waste no time in trying to throw a roadblock in its way. The sales tax bill, up for debate on yesterday's calendar, was the nearest available roadblack.

So, in an abrupt series of moves, which prompted Senate President Steny Hoyer to rush into the Senate aisles to plead with them, Sens. Charles Gilchrist, Laurence Levitan, Victor L. Crawford and C. Lawrence Wiser all announced they would vote in favor of the sales tax cut, the passage of which would deprive the tax relief legislation of the funds needed to sustain it.

But the immediate effect of their action was to breathe unexpected life into the sales tax cut move. By a 25-to-20 vote, with the Montgomery County bloc casting the deciding votes, the Senate overrode the action of its own Budget and Taxation Committee and brought the bill to the floor for debate.

"Now we've got some leverage," said Crawford, one of the renegade four, as he sat in the Senate lounge smoking a cigar shortly before the crucial vote was taken. "If we can (revive) this (the sales tax cut), no other legislation can move . . .

"(Acting Gov. Blair) Lee hasn't been talking to the Montgomery senators about the (proposed) tax package. Steny isn't talking to us. Nobody's talking to us."

He puffed his cigar a moment and watched as two harried administration lobbyists huddled with some of his Montgomery County colleagues in the Senate corridors.

"They're talking to us now," he said.

The quick turnabout of Sens. Crawford, Wiser, Levitan and Gilchrist - all of whom had voted in favor of the sales tax last year - apparently came as an unpleasant surprise to both Hoyer and Lee yesterday.

"We knew the natives were restless, but we didn't know they were this restless," one Lee aide commented as the two-hour debate over the sales tax cut bill continued. And after the vote, Hoyer's administrative assistant, Bruce Bereano, conceded that "this was not expected.

"But I think a couple of senators are going to switch back," he said. A Lee aide, who asked not to be quoted, agreed with Bereano's general sentiment. "It's a problem; it's not insurmountable."

The effort to win the dissident four senators back into the leadership's fold began almost as soon as they had made their move. Less than half an hour after Levitan announced his intention to vote in favor of the sales tax cut measure, he was ushered upstairs to the acting governor's office for a discussion of the county's problems.

"Hold them for a while, I'm going upstars," Levitan called over his shoulder to fellow dissident Gilchrist as he and Del. Donald L. Robertson, head of Montgomery County's House delegation, headed to Lee's office.

Shortly after Gilchrist announced that he would support the sales tax cut "until I have a better idea where the leadership (tax relief) package is going," Hoyer turned over his gavel to Sen. Harry J. McGuirk (D-Baltimore) and rushed to the Montgomery County corner of the floor to quietly expostulate with the four senators.

As the day ended in favor of the sales tax cut, those who had at the last moment found allies in the disgruntled Montgomery County senators were claiming, along with sales tax cut opponents, that they had enough votes to carry the day. Just who will win, however was to be decided sometime today, when the revived sales tax cut bill comes up for a preliminary vote.