WASHINGTON — The National Rifle Association is using a Justice Department memo it obtained to argue in ads that the Obama administration believes its gun control plans won’t work unless the government seizes firearms and requires national gun registration – ideas the White House has not proposed and does not support. The NRA’s assertion and its obtaining of the memo in the first place underscore the no-holds-barred battle under way as Washington’s fight over gun restrictions heats up. The memo, under the name of one of the Justice Department’s leading crime researchers, critiques the effectiveness of gun control proposals, including some of President Barack Obama’s. A Justice Department official called the memo an unfinished review of gun violence research and said it does not represent administration policy. The memo says requiring background checks for more gun purchases could help, but also could lead to more illicit weapons sales. It says banning assault weapons and high capacity ammunition magazines produced in the future but exempting those already owned by the public, as Obama has proposed, would have limited impact because people now own so many of those items. It also says that even total elimination of assault weapons would have little overall effect on gun killings because assault weapons account for a limited proportion of those crimes. The nine-page document says the success of universal background checks would depend in part on “requiring gun registration,” and says gun buybacks would not be effective “unless massive and coupled with a ban.” The administration has not proposed gun registration, buybacks or banning all firearms. But gun registration and ownership curbs are hot-button issues for the NRA and other gun-rights groups, which strenuously oppose the ideas. Justice Department and White House officials declined to provide much information about the memo or answer questions about it on the record. The memo has the look of a preliminary document and calls itself “a cursory summary” and assessment of gun curb initiatives. The administration has not released it officially. But the NRA has posted the memo on one of its websites and cites it in advertising aimed at whipping up opposition to Obama’s efforts to contain gun violence. “Last month, White House spokesman Jay Carney said none of Obama’s proposals “would take away a gun from a single law-abiding American.” Other administration officials have said their plans would not result in gun seizures or a national gun registry.