It all happened yesterday with amazing, almost stunning, swiftness.

On Tuesday, only 24 hours before, a number of unwieldy obstacles still seemed to block the way of the delicately balanced package of property tax relief that legislative leaders are trying to push through the General Assembly.

Then, by last night, all of these obstacles seeme to have miraculously dissolved, and the tax relief legislation seemed to be barreling along through the legislature with a momentum that surprised even some of its most ardent backers.

"I wouldn't be surprised now if we got 100 votes in the House," Del. Benjamin L. Cardin (D-Baltimore) said yesterday. "I'll even predict that we get more than 100 votes," added the young chairman of the House Ways and Means Committee, who played an integral role in putting the tax relief package together.

Cardin had reason to be optimistic. For the past two weeks, he and House Speaker John Hanson Briscoe had been decidedly cautious when asked to predict how the legislation would fare in the General Assembly.

Seven separate bills needed to win approval in both the House - which seemed to favor the package - and the Senate - whose members seemed skeptical. Furthermore, the measures needed to pass through both houses relatively free of amendments, since any untoward amendment could tip the delicate balance of the package and sent it all crashing down.

Finally, the package needed the signature of Acting Gov. Blair Lee III - the man who has been a staunch opponent of one of the crucial elements of the legislation.

Yesterday, almost all the opposition on these fronts seemed to collapse.

Until yesterday, the most intractable obstacle blocking the legislation was a band of seven rebellious senators from Montgomery County. These legislators, feeling that their constituents had been shortchanged when the tax relief package was formulated, had unexpectedly united last week in support of another piece of legislation that would have done away with $133 million in state reveneus.

Without this money, the property tax relief package, which will cost the state more than $50 million, could not have been implemented.

Late on Tuesday night a deal was struck and the opposition of the Montgomery County senators dissolved. The legislators had objected to a police aid bill in the tax package that would have given about $4 million each to Baltimore and Prince George's County, while giving Montgomery County little more than $1 million.

They were placated, however, when Lee reported to them Tuesday night that state revenue collectors had unexpectedly found $3.5 million in revenues that had not yet been allocated.

At a Tuesday night meeting, which included the dissident Montgomery County lawmakers, legislative leaders, and Lee, it was decided that $1 million of this money would go to Montgomery County.

"As a result of this, Montgomery County feels the inequities in the package have been at least partially adjusted," Sen. Victor L. Crawford (D-Montgomery) said yesterday.

"We acted as a bloc for the first time and proved that when you act as a bloc you can redress some of the inequities you might otherwise suffer," Crawford continued during the press conference called by the Montgomery legislators yesterday.

The roadblock legislation that the Montgomery County senators had supported - legislation designed to repeal last year's one cent increase in Maryland's stte sales tax - was defeated in the Senate yesterday by a vote of 20 to 25. Sen. Howard Denis (R-Montgomery), a co-sponsor of the legislation, joined his fellow Montgomery Countains in voting against it.

With that vote, the momentum of the property tax package seemed to pick up dramatically. Earlier in the day, Cardin had obtained preliminary approval from his House colleagues for all seven bills in the package, and the only amendments tacked onto the legislation were amendments that Cardin himself had approved.

Then, late in the afternoon the state Senate, where the tax relief legislation was expected to have a hard time, give overwhelming approval to two key elements.

Tbe biggest surprise came when the senators, by a 33-to-12 vote, gave preliminary approval to the tax credit bill, a sweeping $33 million measure designed to tie property tax relief to homeowner's income.

This tax credit legislation, favored by legislative leaders, has repeatedly been condemned by Lee, who was pushing himself instead his own measure to roll back assessments on private homes across the state by 5 percent. This measure represented a potential 10 percent savings for state homeowners.

Earlier this week, however, Cardin effectively tied Lee's hands on the issue by making the passage of Lee's rollback bill contingent on the passage of the tax credit bill.

Yesterday, one day after Cardin had linked the two pieces of legislation, Lee signaled his tacit approval of the package by sending down a supplemental budget, which included the revenues necessary to finance the tax relief legislation.

This action by Lee seemed to be the final sign that legislative leaders needed to reassure them that the package they had worked so hard to put together would probably manage to make its way through the legislature unscathed.

"For the time being we have eliminated any geographical opposition," said Cardin, who had played a key role in placating the angry Montgomery senators with the extra $1 million.

"This package really developed as a result of going to every delegation in the House of Delegates and finding out what they wanted," Cardin continued. "We went to every delegation, even the minority (the Republicans). We listed to everybody. We didn't agree with them all," he added.

Earlier, when defending his bills on the floor of the House of Delegates, Cardin had declared, "politics is the art of compromise . . . there are parts of this package that a number of people don't like. But this program does involve meaningful property tax relief for everybody."