The Treasury Department would enjoy a 14 percent increase, to $135.1 billion, in appropriations under President Reagan's fiscal 1984 budget.

In the part of the budget the department can control, substantial increases would show up in offices that have law enforcement responsibilities. The Internal Revenue Service, Customs Service and Bureau of Alcohol, Tobacco and Firearms (BATF) are all part of the administration's nationwide war on drug trafficking by organized crime, an effort that would receive 30 percent more funding in fiscal 1984.

Overall, the IRS budget would decrease from $6.4 billion to $6.3 billion. But the agency would increase funds for tax return examination and tax litigation from $1 billion to $1.3 billion. Funds for investigations, tax collection and taxpayer services would increase from $767 million to $1 billion, and the number of full-time employes working in that area would grow to 27,892, compared with 24,542 in fiscal 1983 and 22,694 in 1982.

BATF, which the administration had wanted to abolish in last year's budget, would receive a 7 percent increase under the latest budget. Funds would increase from $147.5 million to $157.2 million, and full-time staff would increase slightly to 2,974, but still well below the 3,671 full-time employes the agency had in fiscal 1982.

While the administration notes its commitment to strong border enforcement and additional money for such programs as one to protect the illegal export of critical technology, the budget for the Customs Service would increase by only 1 percent, from $571 million to $578 million. Funding for the Secret Service, however, would increase 13 percent, from $240.5 million to $270.8 million.

Revenue-sharing funds would hold steady from this year to next, at $4.6 billion.