The Reagan administration yesterday split ranks with the National Rifle Association and a Senate subcommittee over the future of the Treasury Department's Bureau of Alcohol, Tobacco and Firearms, which is responsible for enforcement of gun laws.

At issue is an administration plan to abolish ATF and transfer its personnel and duties to other agencies within Treasury. The Secret Service would oversee firearms, explosives and arson enforcement, and the Customs Service would handle alcohol and tobacco regulation.

Abolition of ATF has long been a goal of the NRA, which has charged that the agency harasses law-abiding gun owners. Under President Reagan, a lifetime NRA member, the organization got its wish, but it had not bargained on the Secret Service taking over enforcement.

In announcing the reorganization, Treasury Department officials promised that the law would be enforced. Gun owners became concerned that the Secret Service might be even more zealous in enforcing gun laws and less vulnerable than ATF to outside attack and influence.

As a result, NRA leaders are in the awkward position of quietly lobbying to undo their accomplishment. Yesterday, a Senate Appropriations subcommittee voted, 4 to 1, to give them what they want.

As NRA President Neal Knox watched intently, the subcommittee approved a plan by Sens. James Abdnor (R-S.D.) and Dennis DeConcini (D-Ariz.) to keep ATF alive.

Under the plan, firearms enforcement responsibility would remain at ATF, but the number of agents doing that job would be cut from 700 to 300, with the extra 400 agents being transferred to the Secret Service for general purposes.

Another 317 agents would go to the Secret Service with explosives and arson authority, and ATF, renamed the "Treasury Compliance Agency," would keep tobacco and alcohol regulation.

Sen. Paul Laxalt (R-Nev.), speaking for the administration, opposed the Abdnor-DeConcini plan and asked for a compromise giving the Secret Service authority for explosives, arson and criminal firearms enforcement and keeping ATF alive with responsibility for regulation of firearms, tobacco and alcohol. He was defeated, 4 to 1.

Warning that the subcommittee plan could lead to reduced enforcement of firearms laws, Laxalt said he will fight to substitute the administration plan in the full Appropriations Committee, probably next week.

Knox said the NRA had given its approval to the subcommittee plan. "There would be fewer agents. That is something that is desirable. They have had more agents than they needed . . . they have dreamed up things to do. In most cases they have been a party to the offense . . . . It's an exact equivalent to Abscam," he said.

"One of our basic concerns with the Secret Service is that the Secret Service has too few agents in election years, but they have too little to do three years out of four . . . . I don't want to see those laws in the hands of people with too little to do," Knox said.