The Reagan administration is considering dissolving the Bureau of Alcohol, Tobacco and Firearms, which regulates licensing of firearms dealers and has been the primary federal agency responsible for investigating illegal cigarette, alcohol and gun dealing, according to bureau officials.

A bureau spokesman said no official word on the bureau's future had been received, but administrators there have told their staffs that a severe reduction in budget and responsibilities has been proposed by the Office of Management and Budget.

Some bureau investigators predicted yesterday that this would end any serious enforcement of federal gun laws, the most controversial of the bureau's responsiblities. Other bureau officials said that the same level of firearms regulation could be continued by other federal agencies even if the bureau were abolished, if the administration chooses, but the administration's plans on that question aren't yet known.

OMB's preliminary decision would eliminate the bureau's responsibility for investigating arson, cigarette smuggling and the theft and illegal transportation of explosives. There would be a deep budget cut in the firearms enforcement area, and the remaining bureau functions would be assigned either to the Internal Revenue Service or the Customs Service, informed sources said.

The bureau was split away from the IRS and established as a separate agency in the Treasury Department by the Nixon administration in 1972 as part of its "war on crime." It has approximately 3,900 employes.

In the firearms area, the bureau has concentrated on the illegal distribution of guns by organized crime, particularly in the New York metropolitan area and in Florida. A Treasury official contended yesterday that the bureau's agents had been an invaluable source of expertise to state and local investigators. The most recent Treasury Department annual summary notes that 1,031 individuals were convicted for violations of federal firearms laws in the 1979 fiscal year.

The bureau is also responsible for licensing firearms dealers and supervising compliance with federal restrictions that bar sales of firearms to minors and convicted felons. Another major activity has been the investigation of bombings and thefts of explosives. It has attempted to perfect a system of "tagging" explosives with chemical codes that could be detected after an explosion to help investigators track down the origin of the explosives.

But a report by the Heritage Foundation prepared for the incoming Reagan administration concluded that significant budget savings could be achieved if the bureau were eliminated as a separate agency and consolidated with the Customs Service. Norman Ture, author of that report and now assistant treasury secretary for tax policy, said the proposal was not motivated by a desire to limit the federal government's enforcement of federal firearms law, but was simply aimed at improving efficiency in government.