The House Interior Committee has approved a three-year $90 million program to preserve the Appalachian trail from the inroads of suburban sprawl and vacation-home development.

It endorsed legislation this week that sends an increased fund authorization measure to the House floor for action.

As originally proposed, the measure called for a one-time outlay totaling $35 million to buy land along the trail. Rep. Goodloe E. Byron (D-Md.) proposed, and the committee supported, outlays of $30 million in each of the next three fiscal years.

The Appalanchian Trail, a facility for hikers, extends 1,995 miles along the East's highest mountain system, from Maine to Georgia. It skirts to the west of Washington, crossing Maryland at a narrow point roughly midway between the cities of Frederick and Hagerstown, and continues southward through Virginia on the east side of the Shenandoah Valley.

The measure authorizes spending, but does not actually provide the money, which must come through a separate appropriation procedure. It contemplates the completion of land-acquisition to fill gaps in the trail by 1980.

Federal spending to acquire trail properties was authorized by Congress in 1968.

In testimony earlier this month, Assistant Interior Secretary Robert I. Herbst said 650 miles of the Appalanchian Trail is located on private land and another 175 miles is along highway shoulders.