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The bill, which Ms. Feinstein said she would introduce in the Senate on Thursday afternoon, would exempt firearms used for hunting and would grandfather in certain guns and magazines. The goal of the bill, she said, would be "to dry up the supply of these weapons over time."

Surrounded by victims of gun violence, colleagues in the Senate and House and several law enforcement officials, and standing near a peg board with 10 large guns attached, Ms. Feinstein acknowledged the difficulty in pursuing such legislation, even when harnessing the shock and grief over the shooting of 20 schoolchildren in Newtown, Conn., last month. "This is really an uphill road," Ms. Feinstein said.

Since the expiration of a ban on assault weapons in 2004, there has been a deep reluctance among lawmakers to revisit the issue. They cite both a lack of evidence that the ban was effective and a fear of the powerful gun lobby, which has made significant inroads at both the state and federal level in increasing gun rights over the last decade.

Senator Harry Reid of Nevada, the majority leader, recently said during an interview in his home state that he was skeptical about the bill. Ms. Feinstein immediately called him to express her displeasure with his remarks.

Many lawmakers, including some Democrats, prefer more modest measures to curb gun violence, like a bill that would enhance background checks of gun buyers or focus on enforcement of existing laws.

One such measure has been introduced by Senator Patrick Leahy, Democrat of Vermont and chairman of the Senate Judiciary Committee, who will begin hearings next week on gun violence. His bill would give law enforcement officials more tools to investigate so-called straw purchasing of guns, in which an individual buys a firearm for someone who is prohibited from obtaining one on his own. While Mr. Leahy has said he supports a limit on magazines, he has expressed skepticism about a broad assault weapons ban. Many gun control groups have set more modest goals, focusing on gun trafficking and the tracking of mental health records.

More legislation is expected to arise over the next week or two. Senator Kirsten Gillibrand, Democrat of New York, and Senator Mark Kirk, Republican of Illinois, have agreed to work together on gun trafficking legislation that would seek to crack down on illegal guns. Currently, there is no federal law that defines gun trafficking as a crime.

Ms. Feinstein was joined on Thursday by several other lawmakers, including Representative Carolyn McCarthy of New York, who will introduce companion legislation in the House, and Senator Richard Blumenthal of Connecticut, who emotionally recalled the day when the children and adults were gunned down in Newtown. "I will never forget the sight and the sounds of parents that day," he said. Several gunshot victims, families of those killed and others gave brief statements of support for the bill.

Ms. Feinstein's bill — which, unlike the 1994 assault weapons ban, of which she was a chief sponsor, would not expire after being enacted — would also ban certain characteristics of guns that make them more lethal and would require that grandfathered weapons be registered. More than 900 guns would be exempt for hunting and sporting.

Such a measure is vehemently opposed by the National Rifle Association and many Republicans lawmakers, as well as some Democrats. "I don't think you should have restrictions on clips," said Senator Tom Coburn of Oklahoma, who has said he welcomes a Senate debate on guns. "The Second Amendment wasn't written so you can go hunting, it was to create a force to balance a tyrannical force here."

President Obama has called on Congress to act on some gun restrictions; on Thursday afternoon, Vice President Joseph R. Biden Jr. was to hold an online "fireside hangout" via Google.