One of the two fuel gauges aboard the WTOP-radio traffic-watch plane that crashed last week, critically injuring WTOP-radio traffic reporter Steve Thompson and a pilot, may have been defective.

Eugene Sundeen, an investigator for the National Transportation Safety Board, said yesterday tests revealed the plane's right fuel gauge mistakenly read one-eight full when in fact the tank was empty. Sundeen, said the other gauge appeared to be working.

Sundeen last week determined there was no fuel in the single-engine Cessna after the crash and records kept by the plane's owner, Colgan Airways Corp. of Manassas, suggested the plane may have run out fuel during its flight.

The plane crashed Nov. 15 in a Vienna neighborhood during evening rush hour. Thompson, 34 of Alexandria, was listed in critical condition at Fairfax Hospital for several days and hospital officials had said they were uncertain he would survive the accident.

Thompson since has improved to the point where he yesterday was listed in serious condition. The plane's pilot, Bernard Wicker, 52 of Gainesville, is listed in fair Condition.

Sundeen said he has been unable to talk about the gauges to Wicker, who had a tube placed in his throat to aid breathing. He said he hopes to interview Wicker next week.

A safety board spokesman said the board's final report on the accident probably would not be completed for at least six months.