Makers and sellers of small handguns known as Saturday Night Specials can be held liable for injuries inflicted with those guns, Maryland's highest court ruled today. The decision could end the sale of cheap handguns in Maryland, both handgun opponents and gun dealers predicted, and could serve as a precedent for other courts around the country.

Handgun opponents have tried unsuccessfully for years to convince courts that Saturday Night Specials, short-barreled guns that are lightweight, easy to obtain and relatively cheap, have no legitimate purpose, and that the people who make them and sell them should know they are sold for criminal purposes.

The Maryland Court of Appeals, in a unanimous opinion, adopted that reasoning and ruled that "the manufacturers or marketers of a Saturday Night Special know or ought to know that he is making or selling a product principally to be used in criminal activity." Such guns are "largely unfit" for legitimate uses, the court stated.

The ruling was requested by the U.S. District Court in Baltimore, which is hearing a $500 million liability suit brought by a Silver Spring grocer against a West German gun manufacturer, Roehm Gesellschaft. The grocer, Olen J. Kelley, was shot with a Roehm .38 during a 1981 holdup of his store. Because the liability issue falls under Maryland Common Law, the federal court will be bound by the court of appeals decision when it tries the Kelley case.

Roehm could ask the Court of Appeals to review the case again or appeal to the Supreme Court. Stephen V. Charles, the attorney representing Roehm, refused to discuss any aspect of the case.

The Maryland court's decision upholds the principle of third-party liability. Under that principle, courts have begun to make rather innovative rulings, finding, for example, that landlords can be held responsible for rapes that took place in their buildings.

The gun decision "is a tremendous breakthrough," said Michael Hancock, a lawyer working with the National Coalition to Ban Handguns, which is assisting Kelley in his suit. "It has the potential for putting manufacturers of Saturday Night Specials out of business . . . . After today, I think that any prudent gun dealer in Maryland would be rather foolish to sell Saturday Night Specials."

Dave Warner, a spokesman for the National Rifle Association, was less pleased with today's decision, but agreed that the impact could prove significant. If a gun manufacturer is going to be held liable, "it will probably have to stop manufacturing those types of guns," he said.

The guns are not used solely by criminals, as is commonly perceived, Warner said. "They are inexpensive, and therefore a useful tool to the people that need them most -- the people that are poor, people that are black, people that are usually affected by crime," Warner said.

Bob Meck, who sells handguns starting at about $70 in his Annapolis gunstore, agreed. "A lot of people on fixed incomes can only afford to put so much into protection," he said. If the court of appeals decision goes unchallenged, he said, "the working-class person making under $15,000 would never be able to afford a gun."

Meck said he has liability insurance and will continue selling cheap handguns, at least for the present. But he predicted today's court ruling could eventually force dealers to concentrate on more expensive gun models.

Howard L. Siegel, the lawyer who represents the Silver Spring grocer, said the court's decision today "will open the floodgates" for liability litigation against handgun manufacturers. "Perhaps the juries -- the citizens -- can do what the legislatures could not," he said.

The appeals court said its liability ruling would only apply to Saturday Night Specials which, because they are inaccurate and unreliable, are "virtually useless for the legitimate purposes of law enforcement, sport, and protection of persons, property and business."

" . . . In light of the ever-growing number of deaths and injuries due to such handguns being used in criminal activity, the imposition of such liability is warranted by today's circumstances," the court said.

Because the definition of a Saturday Night Special is not clear-cut, the court said, it would be up to a judge or jury hearing a liability case to decide whether a gun fell into that category. Liability would only exist, the court added, when the victim suffered injury or death in a shooting.

Handgun dealers said Roehm is one of the major manufacturers of inexpensive handguns sold in the country. The gun that John Hinckley Jr. used to shoot President Reagan was a Roehm-RG14. The gun used in the 1981 Silver Spring shooting, an RG-38S, is not currently advertised in gun magazines but was listed in 1982 at between $35 and $55. Other models of Roehm revolvers currently sell for about $70, according to advertisements in gun magazines.