WASHINGTON — Vice President Joe Biden said Thursday that he is more concerned about limiting the number of rounds in a gun magazine than about banning semiautomatic firearms that account for a small percentage of gun deaths.

Biden argued that the shooter at the Sandy Hook Elementary School in Newtown, Conn., could have been slowed down if he had fewer rounds in each magazine and had to change clips more often.

“Maybe if it took longer, maybe one more kid would be alive,” Biden said during an online video chat on Google Plus.

The vice president led a White House gun control task force in the wake of the Newtown shooting last month. President Barack Obama said last week after Biden completed the review that he wants Congress to require background checks for all gun sales and ban military-style semiautomatic firearms and high-capacity ammunition magazines.

The president conceded that passage will be difficult, with support for gun-ownership rights strong among lawmakers.

Biden said he wants a ban on assault weapons, even though he acknowledges that they don’t account for a large portion of gun deaths in America. He said a ban would solve part of the gun-violence problem, particularly for police who can be outgunned by criminals with such weapons.

“It is not an answer to all the problems,” Biden said. But he said he views an assault-weapons ban as “a rational limitation on what type of weapons should be owned.”

Biden’s comments came on the same day that a group of Democratic lawmakers, led by Sen. Dianne Feinstein of California, reintroduced legislation to ban assault weapons and magazines over 10 rounds. At a news conference backed by police officials, mayors and crime victims, the lawmakers acknowledged the heavy lift ahead to get the legislation through Congress.

“If anyone asks today ‘Can you win this?,’ we don’t know, it’s so uphill,” Feinstein said.