The Maryland General Assembly apparently unwittingly legalized the return of slot machines in Calvert County in the closing days of the 1977 legislative session.

The accidental enactment was discovered last week by Elizabeth Buckler, an assistant legislative officer whose job it is to read every word of every bill.

At first blush, it appeared that Buckler had uncovered what her boss, Alan M. Wilner, Gov. Marvin Mandel's chief legislative officer, thought was "the snake of the century," a snake being legislative jargon for a word or clause that sneakily distorts the intention of a bill.

"That wasn't your ordinary snake, it was a damned anaconda," Wilner said, noting that Mandel would probably veto it.

The few words that apparently opened the door to the return of slot machines were detected on page 53 of a 69-page bill that was filled with technical changes on dozens of local laws affecting stray dogs, elections, garbage collection and fence heights and plumbers' licenses.

The sponsor of the bill, Del. Thomas A. Rymer (D-Calvert) said yesterday that he had "no intention to legalize slots" in his county, although he favors their return. "But I wouldn't want to do it through the back door," said Rymer, a former state's attorney.

Since the last legal slot machines disappeared from Maryland in 1968, there have been annual attempts to get the legislature to bring them back. But while supporters cited the economic gains that benefited areas that had them - at one time there was a slot machine for every 13 people in Charles County - opponents contend that they also brought crime and corruption.

Rymer said he had been assured in writing by the drafter of the bill, F. Carvel Payne of the state's Department of Legislative Reference, that the proposal contained "no substantive changes" from existing law.

Rymer didn't know that the bill revived slot machines until he was contacted by a reporter yesterday, he said.

"That was a slick little deal, wasn't it?" he said laughing. "A cute little local snake," Rymer continued.

Payne, the chief bill drafter for the General Assembly, insisted that the language of the bill he wrote does not permit the return of slots, but others disagree.The language in the bill "clearly re-enacts" an old county law legalizing slots, said Deputy Attorney General George Nilson.

Wilner waid he informed Mandel, an aficionado of legislative maneuvering of "this beautiful little snake" during a review of a stack of bills at the Governor's Mansion on Tuesday.

The ailing governor, a snake fancier of long standing, "thought it was one of the funniest things he'd ever heard," Wilner said.

Unless the governor gets an opinion from the attorney general's office that the bill does not permit the return of slots to Calvert County, Mandel will veto the bill, Wilner said.

Slots machines were legalized in Calvert County in 1949, after voters approved their use by a 2-to-1 vote. The one-armed bandits became an important source of revenue to Calvert and three other rural counties in Southern Maryland (St. Mary's, Anne Arundel and Charles) until they were outlawed in 1968 by a state law.

The old local law, however, remained on the books in Calvert, although it carried no force because it had been superseded by the state action.

But when Rymer asked the state's legislative reference bureau to update and clarify the county's local laws, Payne chose merely to reword the old slot machine law instead of deleting it. In so doing, the new local law superseded the state law that banned slots, and apparently set the stage for their return in Calvert County.

The apparent mix-up went undetected as the bill worked its way through the legislature.After Rymer introduced the bill in the House on Feb. 21, it was assigned to the select committee that considers bills that affect only Calvert County. And because Rymer is the only delegate from Calvert, the bill zipped through the House without discussion.

In the senate, it was similarly assigned to the one-man Calvert delegation there, where it emerged with a number of amendments, but none that affected the so-called gaming section.