Five months ago, with Maryland's savings and loan industry on the brink of collapse, Gov. Harry Hughes called seven sweeping measures enacted by a special session of the General Assembly "a milestone" in solving the industry's problems.

Today, on the eve of what was promised to be another milestone in that passage, Hughes' effort to return the industry to normal is in a shambles, torpedoed by the state Senate and its leader, Melvin A. Steinberg. The milestone has turned to a millstone.

Steinberg stunned the governor today by rejecting the deal that Hughes had negotiated with Chase Manhattan Corp. for the purchase of Merritt Commercial Savings and Loan Association and two other thrifts. Facing a deadline to approve the deal, Steinberg said too many questions were unanswered.

Estimates by Chase and the administration of the liability the bank would assume changed daily. Valuations of the properties Merritt owner Gerald Klein would receive were called into question. Documents promised by the administration and Chase were never delivered.

The deal, said Steinberg privately, had a "smell" about it.

Hughes predicted last week that with passage of the Chase deal "we will have narrowed our problem down to maybe one or two major problems," an obvious reference to Old Court Savings and Loan and Community Savings and Loan, which remain under conservatorship. Now he is staring into a fiscal and political black hole.

The governor's hopes began crumbling last week when negotiations for a Citicorp subsidiary to acquire beleaguered First Maryland Savings and Loan broke off and the damage expanded today to Merritt, Friendship and Chesapeake savings and loans.

Hughes appears now to be paying the price of keeping the legislature at arm's length during the long negotiations with Chase. Although Steinberg and House Speaker Benjamin L. Cardin were briefed, there appears to have been little thought given to the politics of the deal, which is where it is foundering.

The Senate's disgust for the deal negotiated by the Hughes administration erupted in full force Tuesday, when senator after senator rose to denounce the arrangement.

"When you are playing high-stakes poker with the likes of Chase you have to go eyeball to eyeball until the other guy blinks," said Sen. Thomas V. Mike Miller (D-Prince George's.) "Harry Hughes didn't just blink, he closed his eyes."

Among the ironies of today's events is that few presidents of the Senate have been able to work their will on that often-unruly body as well as Steinberg. Through sheer force of personality, many members said, Steinberg could have forced through a deal that he vociferously defended as late as Tuesday night, when he thundered at his leadership behind closed doors to support the legislation. But faced with overwhelming opposition among the Senate leadership and his own nagging concerns, Steinberg decided to change course this morning.

Probably no one was more surprised than Hughes, who has come to depend on the Baltimore County legislator. Asked by one of his colleagues about Hughes' reaction, Steinberg said simply, "He gulped."

For Hughes, the supreme irony is that after overcoming disastrous relations with the legislature during his first term to the point that the first and second floors of the State House worked harmoniously, he is now faced with open revolt on an issue of critical importance.

For the Senate president, his stance will bring enormous political heat. But Steinberg is not running for anything besides another term in his comfortably safe seat, and his colleagues say he has their support.

The impact is unpredictable for Hughes, who has slogged through the savings and loan crisis for five months, predicting all the while that the light was at the end of the tunnel. Now that the Chase deal is apparently dead, Hughes can claim, with some justification, that his fingerprints are not on the corpse. The distinction, however, may be lost on Maryland citizens who have watched a savings and loan crisis deteriorate rather than improve.

One Washington lawyer whose firm specializes in representing savings and loans recently compared Hughes' statements on the problem to President Nixon's frequent proclamations of victory in Vietnam.

"The governor announces victory every month and there is no victory," the lawyer said. "It just gets worse."