Washington ? Gun owners may have no better ally in Washington than Atty. Gen. John Ashcroft, once featured in a National Rifle Assn. magazine cover story as “a breath of fresh air” in the capital.

Now that Ashcroft’s Justice Department has taken over the Bureau of Alcohol, Tobacco, Firearms and Explosives, gun control supporters are concerned he could begin chipping away at enforcement rules.

They say the switch gives Ashcroft the opportunity to weaken oversight and regulation in such areas as federal licensing for gun sellers, how banned assault weapons are defined and whether to expand a ballistics matching system that traces guns used in crimes.

“You have the most pro-gun attorney general in history taking over the reins of the ATF,” said Matt Nosanchuk, litigation director of the Violence Policy Center, a nonprofit gun control research group. “It really is a cause for concern.”

Justice Department officials said Ashcroft was focused on prosecuting criminals, not weakening gun laws.

“We are very aggressively enforcing the nation’s guns laws and will continue to do so,” Adam Ciongoli, a senior Ashcroft ad-viser, said Wednesday.

Justice officials say their emphasis on gun prosecutions was underscored by this week’s 87-count indictment against 26 people in Norfolk, Va., accused of running a scheme that brought weapons easily purchased in Virginia to the streets of New York City and other cities.

The ATF has roots in the Treasury Department going back to 1789, with a history including Eliot Ness and the “Untouchables,” who enforced Prohibition and helped bring down Chicago mobster Al Capone.

Under the government reorganization that created the Homeland Security Department, the ATF shifted almost entirely to Justice. Its 4,700 agents, inspectors and others — with expertise ranging from firearms to arson to bombs — are being integrated with the rest of federal law enforcement, notably the FBI.

The only duties that remain with Treasury are alcohol and tobacco tax collections.

Ashcroft, who visited the ATF’s headquarters Wednesday, told reporters that the change would improve law enforcement. He said one of the ATF’s main jobs is to “aggressively enforce firearms legislation and explosives laws which are vital to the security of the American people.”

Gun control advocates remain wary of Ashcroft at ATF’s helm, pointing to these gun-related actions during his tenure:

l Ashcroft reversed Clinton administration doctrine by declaring in 2001 that the right to keep and bear arms under the Second Amendment applied to individuals, not groups such as the “well-regulated militia” cited in the amendment.

l The Justice Department is seeking to reduce from a proposed 90 days to one day the length of time that gun buyer instant background check records are kept by the FBI.

l The department refused an FBI request to check gun purchase background records to determine whether any people detained immediately after the Sept. 11 attacks had bought firearms.

“You’ve got to wonder what his commitment is going to be to regulate guns in this country,” said Eric Gorovitz, policy director of the nonprofit Coalition to Stop Gun Violence.