Environmentalists told a House Interior subcommittee yesterday that the Reagan administration is using the budget to circumvent the law requiring new strip-mining practices across the nation.

The administration's Office of Surface Mining is skimping on inspectors and has "decided to surrender to the coal industry and embark on a program of regulation gutting," said Edward Grandis of the Environmental Policy Center, a nonprofit lobby group here.

The proposed 1983 budget for federal strip-mining activities is $159.8 million, down just slightly from $160.6 million this year. While the environmentalists, who represent citizens groups in mining areas, are not asking for overall budget increases, they want more money to be spent on forcing the states to comply with strict reclamation standards and less on internal reorganization and rewriting regulations.

The agency's "obsession for regulatory 'relief' has set them back a year from any substantive work and has allowed the industry to return to prehistoric mining activities," said Grandis, who was instrumental in the passage of the 1977 strip-mining act.

James R. Harris, director of the Office of Surface Mining, vigorously defended his program.

"There's no way I could attempt to answer what I feel are misguided allegations," he said. "Ours is a very workable budget which addresses itself to the changing role of OSM" as states take over responsibility from the Interior Department.

"If the states are not carrying out the law , I won't hesitate to go in and enforce with federal inspectors," Harris said, citing a recent case against Oklahoma.

Praise for Harris' efforts came from an unexpected quarter.

Arizona Democrat Morris K. Udall, chairman of the Interior Committee who is known as "the father" of the strip-mining law in Congress, said in an interview after the hearing that "Harris has impressed me. He was fairly friendly with the coal people in his state. I thought he came in with a mandate to torpedo the program. But it has not been the clearcut hatchet job I'd feared."

Udall said environmentalists' criticisms are partly correct and that his committee is likely to recommend additional money for enforcement. However, he added that Harris has "come up with some pretty good answers" to criticism on the complex legal and technical problems involved in forcing industry and states to restore strip-mined land.

L. Thomas Galloway, an Environmental Policy Center attorney, criticized the agency's proposal to employ 69 inspectors nationwide who would supposedly inspect 4,800 industrial sites a year, 17 percent of all sites.

The number of inspectors required to do a minimal job, the number of mines, the number of visits necessary, and the number of likely enforcement actions are "significantly understated," Galloway said. Virginia officials have allowed coal operators to circumvent the law by claiming they were mining exempted two-acre units, he added.

Charles Shetekoff of the Illinois South Project, a nonprofit group of environmental, farm, church and civic activists based in Herrin, Ill., called on Congress to "put an end to the abuses of this administration." He said they had all but dismantled regional enforcement programs in Illinois, Indiana and Ohio, which he described as inadequate to begin with.

Coal mining in southern Illinois has taken place on prime farmland, and has been a source of continuous controversy.