After months of rumors and high-level meetings, the Treasury Department is expected to announce within the next week that it is eliminating the Bureau of Alcohol, Tobacco and Firearms (BATF) to save money.

Sources at BATF and on Capitol Hill said they had been told that Treasury Secretary Donald T. Regan decided Wednesday to abolish the agency and that the announcement could come at any time.

But Marlin Fitzwater, a spokesman for the Treasury Department, said the final decision probably will not be made until next week.

Word first leaked in September that the administration had decided to eliminate BATF, which enforces federal gun laws, along with 30 to 40 other agencies, boards and commissions.

The administration had recommended that the bureau's budget be cut to $120 million this fiscal year, down from last year's $150 million.

But there have been accusations, both from BATF officials and on Capitol Hill, that the agency had been targeted for political reasons as well. The National Rifle Association, claiming that BATF agents have harassed law-abiding gun owners, have waged a long campaign to abolish the agency.

One House source said yesterday, "They may say they're doing it to save money, but they're doing it because the NRA has been after this outfit for a long time. They're not going to disband their functions."

Sources at BATF say they have been told that the Secret Service will take over the agency's responsibilities for firearms, arson and explosives, and that the Customs Service will take over enforcement of cigarette and alcoholic beverage regulations.

Fitzwater said high-level Treasury officials met yesterday to study possibilities for absorbing some of the agency's 3,500 employes into those agencies and the Internal Revenue Service, but added, "There are enough obstacles and problems that it's still possible that won't happen."

He said he had no idea how many jobs would be lost in the reorganization.

One House staff member said he had been told that BATF agents have already been ordered not to start any new cases and that their travel money has been cut over the past several weeks.

James Lynch, a BATF spokesman, yesterday confirmed that five of his agency's offices around the country have been shut in the past few months.

A House Judiciary subcommittee attempted to confront the administration last month on its plans for phasing out the agency.

Rep. William J. Hughes (D-N.J.), chairman of the crime subcommittee, produced a memo signed by Assistant Treasury Secretary John M. Walker dealing with "how and where" the bureau would be broken up.

Walker told the committee that, although the language in the memo had perhaps been "ill-advised . . . , no final decision has been made by the department to dismantle or abolish BATF."