WASHINGTON — Senators pushing to renew a 10-year ban on military-style assault weapons showcased their backing from law enforcement officials on Monday as the Senate headed toward a series of politically charged votes on gun issues.

Senators on both sides of the fight said they expected a close vote on Tuesday on whether to maintain the ban, which is scheduled to expire in September. The ban is being considered as part of legislation granting gun manufacturers and distributors immunity from civil lawsuits arising from gun crimes.

With the outcome uncertain on the assault weapons ban and other gun issues, Sens. John Edwards of North Carolina and John Kerry of Massachusetts planned to take a break from the campaign for the Democratic presidential nomination to vote to extend the ban.

President Bush has said he favors a renewal of the assault weapons restrictions. But he has also called for the legislation shielding the gun industry to be kept free of additional provisions that could slow its progress through Congress.

"The semi-auto ban, the gun-show loophole, a variety of other kinds of issues could simply drag this bill down," said Sen. Larry E. Craig, R-Idaho. Craig is the chief sponsor of the proposal to protect the gun industry from lawsuits seeking to hold manufacturers and dealers responsible for gun crimes and accidents. The measure would allow claims for defective products.

In addition to the vote on assault weapons, the Senate could face amendments that would require background checks for those who buy weapons from private dealers at gun shows and lift the ban on gun ownership in Washington, D.C.

Sen. Dianne Feinstein, D-Calif., said backing for the ban was broad throughout the nation's law enforcement community. "They know the streets of our country will be safer without assault weapons," Feinstein said.

Many Republicans oppose the extension of the ban on assault weapons. But some Republicans were breaking with their party, including Sen. John W. Warner of Virginia.

"These assault weapons are not needed by any hunters, any sportsmen, particularly in this changed world we live in," Warner said.

Supporters of the ban cited an analysis of Justice Department figures indicating that law enforcement requests for traces of assault weapons had declined significantly since the ban was enacted in 1994. They called this evidence that the use of the guns in crimes had dropped. But opponents of the restrictions said that the data was misleading and that the ban was an infringement on gun ownership rights.'

"It's a waste of regulation," Sen. Bill Frist, the majority leader, told news organizations in Tennessee, his home state. "It's not been demonstrated to do anything in terms of making the world a safer or better place."

In a preliminary vote that demonstrated the level of support for the proposal to grant immunity from lawsuits, senators easily defeated a proposal on Monday to broaden the ability to file defective product suits against gun manufacturers.

The White House spokesman, Scott McClellan, said Bush viewed the measure before the Senate as part of the administration's push for legal reforms.

"It's about stopping frivolous lawsuits," McClellan said. "The president believes that the manufacturer or seller of a legal product should not be held liable for the criminal misuse of the product by others."