The Interior Department asked a House subcommittee yesterday to approve $35 million in U.S. aid to help preserve the Appalachian Trail from the inroads of suburban sprawl and vacation-home development.

The department's position, voiced by Assistant Secretary Robert L. Herbst, was supported by Rep. Goodloe E. Byron (D-Md.) and by a coalition of environmental groups at a hearing before the House Interior Subcommittee on National Parks.

The Appalachian Trail, a facility for hikers, extends 1,995 miles along the East's highest mountain system, from Maine to Georgia. It crosses Maryland at its narrowest point, near where the Shenandoah River joins the Potomac - an area of intensive population growth.

"Nine years after passage of an act designed to assure a permanent place for the Appalachian Trail in our national system of parks and recreational preserves, 650 miles . . . are on private land without a legal right to remain and another 175 miles follow roads for lack of a protected right-of-way," Herbst testified.

"Threats to the integrity of the trail are widespread, from second-home development and from the effects of suburban sprawl," Herbst said, noting that he visited and hiked the trail in May.

Pending legislation would grant $35 million a federal funds for land acquisition.

Instead of outright federal grants for such purchases, Herbst said the Interior Department supports that "one-half or $17.5 million of the $35 million be for direct federal acquisition, and one-half or $17.5 million be reserved to provide matching grants to the states" for their own purchases.

"In this way, potentially $52.5 million counting state matching funds, would be available to protect the trail," he said, providing enough funds to preserve 300 miles. The trail corridor would be up to 1,000 feet wide.

Support for the legislation came also from the National Parks and Conservation Association, the Sierra Club, the Wilderness Society, the National Audubon Society and the Defenders of Wildlife.