Sen. Kirsten Gillibrand (D-N.Y.), the one-time vocal gun rights advocate, will vote against an amendment to the Defense authorization bill that would allow owners to carry concealed firearms across state lines.

“I urge my colleagues to oppose this harmful measure and side in favor of law enforcement and state’s rights,— Gillibrand said Tuesday in a statement on the amendment being sponsored by Republican Policy Committee Chairman John Thune (S.D.).

“I strongly believe that the gun laws that are right for New York are not necessarily right for South Dakota, and vice versa,— she added.

Appointed in January to fill the seat vacated by Secretary of State Hillary Rodham Clinton, the former House Democrat once touted sleeping with two rifles under her bed and enjoyed an “A— rating by the National Rifle Association. Gillibrand, who is running to retain her seat in 2010 and could face a challenge from gun control advocate Rep. Carolyn Maloney (D), formerly represented a rural, upstate House district.

In her Tuesday statement, Gillbrand argued that Thune’s amendment unfairly trumps state gun laws.

“It is wrong for the federal government to overrule a state’s ability to enact reasonable, constitutional gun laws designed to prevent criminals and other violent and dangerous persons from carrying guns in city streets,— she said.

Another New Yorker, Conference Vice Chairman Charles Schumer (D) is heavily courting Democrats to vote down the measure, which will likely be considered on the floor Wednesday. To defeat the amendment, Democrats need at least 41 Members to vote “no.—