The National Transportation Safety Board, acting after a spectacular on-the-ground airplane fire last week in Hot Springs, Ark., yesterday recommended immediate inspections of a popular commuter airliner.

In a letter to the Federal Aviation Administration, the safety board said that hydraulic fluid and oxygen lines located close to an electrical circuit panel in the cockpit of the Swearingen SA 226-TC Metro should be examined. The board cited the Hot Springs fire and a similar incident last October at Palm Springs as reasons for the inspections.

The FAA is studying the board's recommendation, a spokesman said.

FAA sources estimate that about 150 of the Swearingen Metro models in question are in service around the country with an unknown number of small airlines.

Commuter airlines typically connect small communities with major airports.

In the Hot Springs incident, a Scheduled Skyways flight carrying two passengers and a crew of two was taxiing for a takeoff. The co-pilot noticed that an instrument light was out, and reset the switch. A spark behind the instrument panel was followed almost instantly by a raging fire. The co-pilot fled his seat and led the passengers out an overwing emergency exit. The pilot turned off the engines and hurried out the front door.

The cause is still under investigation, but in the similar incident in Palm Springs, investigators found that leaky hydraulic fluid lines, combined with escaping oxygen, had been ignited by an electrical spark.

In that case, also on the ground, 16 passengers and two crew members from a Sun Aire flight escaped safely; the plane was badly damaged. Aviation sources said both situations would have been much more critical had they occurred while the planes were airborne.