Senate leaders failed yesterday in an initial attempt to hasten passage of legislation to expand the federal death penalty and ban most semiautomatic assault weapons, but they predicted success in a second attempt planned Thursday.

In a preliminary vote as members straggled back from their Memorial Day recess, the Senate failed by six votes to invoke cloture, which would help to weed out many of nearly 250 amendments that have piled up in what appears to be an effort to delay passage of the measure.

The vote was 54 to 37 in favor of limiting debate. Nine senators were absent, including several considered likely to vote for cloture on the next try.

In addition, Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) said some members who voted against the bill yesterday have indicated that they may support it Thursday now that "they have given the NRA {National Rifle Association} their one vote" on the issue.

The NRA is vigorously opposing the partial ban on assault weapons, which was approved by the Senate by one vote May 23, and critics accuse the lobbying group of trying to bog down the whole measure in amendments. "They lost on guns and, poof, 200 amendments," Biden said.

With yesterday's vote demonstrating that cloture is achievable, Majority Leader George J. Mitchell (D-Maine) scheduled another vote Thursday and said he believes he will have at least 60 votes then. Biden agreed but, in an apparent attempt to rally support among death-penalty advocates, warned that the bill will probably die if cloture cannot be invoked.

The measure authorizes the death penalty for 30 federal offenses, primarily murder, espionage and treason and bans manufacture and sale of nine types of assault weapons most frequently used in violent crimes. It also would ease restrictions on use of illegally obtained evidence in court and restrict appeals by death-row prisoners.