Senate Democrats have dropped the ban from the gun control package they plan to consider next month. However, Biden reiterated Thursday that the White House is still pushing for the measure.
Biden said the president's gun proposals don't infringe "one iota" on Second Amendment rights.
Biden also was joined by Mayor Michael Bloomberg. He emphasized proposals for expanding background checks of gun buyers.
Bloomberg and Boston's Thomas Menino head a coalition called Mayors Against Illegal Guns.
In Washington, gun control advocates were pressing Democrats to broaden background checks for firearms purchases in the gun bill the Senate debates next month, saying it is the strongest step lawmakers can take to produce meaningful legislation.
With the proposed assault weapons ban looking all but dead, groups favoring restrictions say expanded background checks are needed following December's school massacre in Newtown, Conn.
Senate aides and lobbyists expect Senate Majority Leader Harry Reid to include wider background checks in the bill, but say he hasn't made a final decision.
The Democratic bill is also expected to stiffen penalties for illegal gun trafficking and expand school safety aid.
Details of the background check language remain unresolved as senators seek bipartisan compromise on expanding the system, which now covers sales by licensed gun dealers.