The D.C. Council's extraordinary decision to make assault-weapon merchants liable for injuries or deaths their guns cause in the city remained in doubt yesterday as Mayor Marion Barry declined to say whether he will sign the bill and strong signs of opposition arose in Congress.

The council bill, which allows shooting victims or their families to seek damages from gun manufacturers and dealers, is without precedent in the country. Approved Tuesday by an 8 to 3 vote, with two abstentions, it has been praised by gun-control advocates as a dramatic step to cripple the gun trade.

Council members said they passed the bill hoping it would slow the pace of District homicides, which number 453 so far this year. But even those who support the bill said yesterday they fear Congress may block it.

"This idea makes eminent sense," said Gary Hankins, chairman of the labor committee of the Fraternal Order of Police. "But I don't give it much chance of getting through Congress. Much milder forms of gun-control legislation have failed there."

Gun dealers expressed outrage with the council bill.

"That's going to be laughed out of court," said David Condon, a gun retailer in Chantilly. "It's just not constitutional."

Dick Gilbert, a gun retailer in Rockville, said he doubts the bill would have any effect on violence in the District because of the size of the underground gun market. He also said it is "ludicrous" to hold a dealer liable for what someone does with a legally sold product.

"That's like holding a car manufacturer with a car that can reach 160 miles per hour responsible for someone killed in an accident," Gilbert said.

On Capitol Hill, there were strong signals yesterday that the council's action will face intense scrutiny. As some Democrats expressed reservations about the bill's prospects, a top aide to Rep. Dana Rohrabacher (R-Calif.), a ranking member of the House District Committee, said approving the measure would be "unconscionable."

"This is something we can't imagine Congress would support," said Rick Dykema, a legislative aide to Rohrabacher. "The council dropped this last year because it had sensitive things before Congress that it wanted passed. But it still has sensitive things -- like getting an increase in the federal payment."

A top aide to Rep. Ron Dellums (D-Calif.), chairman of the District Committee, said the congressman would support the council bill in defense of home rule, but he added that the pulse of Congress "was difficult to judge."

The council's gun-liability bill comes a month after the National Rifle Association, one of the most powerful lobbying groups in Washington, claimed victory in its latest fight with Congress over gun-control legislation.

This fall, Congress scrapped three Senate moves to ban some semiautomatic assault weapons in favor of a House measure, supported by the NRA, that protects U.S. gun manufacturers who produce those weapons.

Before their vote Tuesday, D.C. Council members expressed concern that Congress would reject the gun-liability bill. The council at first considered making all handgun merchants liable for shooting injuries or deaths in the District, but in a bid to placate Congress it opted to limit the bill to cover only some semiautomatic assault weapons such as the Uzi, Tec-9 or Mac-10.

Council members said the District's surging homicide rate left them no choice but to pass the bill. "I'm sick and tired of seeing blood run down our streets," said council member Frank Smith Jr. (D-Ward 1). "And I believe this will make these sellers think twice before handing weapons over."

D.C. Police Chief Isaac Fulwood Jr. said through a spokesman yesterday that he supports the council's decision. "He welcomes any legislation designed to stem the flow of guns and related violence," the spokesman said.

The council gave the District one of the most strict gun-control laws in the country in 1976 when it banned the sale of all guns. Yet since Janaury 1988, as homicides reached record levels, police have recovered about 8,500 guns and traced 70 percent of them to distributors in Maryland and Virginia.

Because gun-liability lawsuits are rare, it is not clear how the council's bill would fare in court. The Maryland Court of Appeals, the state's highest court, upheld a suit against a manufacturer of inexpensive handguns in 1985, but the state legislature enacted a law that effectively overrode the ruling.

Last year, the D.C. Court of Appeals ruled that selling handguns was "not dangerous in and of itself, but rather the result of actions taken by a third party." It dismissed a suit against a gun manufacturer that was filed by former White House press secretary James S. Brady and a D.C. police officer, both wounded in the 1981 attempted assassination of President Reagan.

When the council first debated a gun-liability bill last year, the city's attorneys said they doubted whether it could withstand court scrutiny. At the time, Barry questioned the wisdom of the bill but said he did not intend to veto it.

Lurma Rackley, the mayor's press secretary, said Barry was studying the new council bill.