WASHINGTON - Changing the rules that allowed 7-year-old Jessica Dubroff to fly an airplane is more complicated than it may seem, the head of the Federal Aviation Administration told a congressional panel yesterday.

''There are a lot of questions involved that are not apparent at the outset,'' such as whether age limits should be set for both young and old, FAA Administrator David R. Hinson told a House Appropriations transportation subcommittee.

Federal aviation rules allow anyone to operate flight controls as long as the plane is under the control of a licensed pilot. It is the pilot's job to protect passenger safety.

Those rules ''have served us very well,'' Hinson said.

But after Jessica's plane crashed last week, the FAA announced it would review the rules. Jessica was trying to set a new record as youngest person to fly across country. She, her father and a flight instructor died in the crash.

As Hinson testified about his agency's budget yesterday, some subcommittee members took the opportunity to lobby him for a change.

''The federal government does not establish any minimum standards?'' asked an incredulous Rep. Richard J. Durbin, D-Ill. ''Let us assume we are dealing with 3-year-olds. At what point is it impractical?''

Hinson responded that changing the rules is tricky because the same rules allow other youngsters interested in flying to experiment. And, he added, if you bar young people from taking the controls, what about old people?

''What's the difference between a 7-year-old and a 97-year-old?'' he asked. ''We want to make sure we have thought about all of these issues. Whatever we do, we want to do it right.''

Durbin countered that no one has a problem preventing children under age 16 from driving.

''That's not a good analogy,'' Hinson responded. The proper analogy, he said, would be a child driving a car with two sets of controls in an open field with no one around for miles.

Hinson also heard arguments for not changing the rules.

''I think the rules are adequate,'' said Rep. Jim Ross Lightfoot, R-Iowa, a licensed pilot. ''You're always going to have someone who pushes the envelope a little bit.''

Lightfoot emphasized that the pilot is in charge of the plane.

''Those people (Jessica and her father) technically were just passengers,'' he said. ''It appears to me there was some poor judgment exercised in that situation.''