The Federal Aviation Administration, trying to prevent a recurrence of crashes like last January's Air Florida accident, is moving to remind airlines that taking off with ice adhering to a plane is illegal and that antifreeze fluids give only partial protection.

A draft "advisory circular" published in the Federal Register yesterday stressed that pilots must visually inspect their planes before taking off in icy conditions.

"If, as a result of these inspections, evidence of ice, snow or frost formations is observed, the aircraft should be returned to a maintenance area for additional de-icing," the draft circular says.

These and other points in the circular underline long-standing rules and appear to reflect concern that pilots may be lax sometimes. The circular, to be distributed later this year as winter flying gets under way, will supplement a 157-page paper on foul-weather flying the FAA sent out last month.

Work on the circular began last year, before Air Florida Flight 90 struck the 14th Street bridge after taking off from National Airport in a snowstorm Jan. 13. But "obviously, the Air Florida accident and the World Airways accident up in Boston gave added impetus to getting these things out," FAA spokesman Fred Farrar said.

Two people were lost and presumed drowned after the World Airways plane, a DC10, skidded into Boston Harbor and broke in two during a foul-weather landing on Jan. 23.

The National Transportation Safety Board has ruled that the Air Florida crew's decision to take off with snow or ice on their Boeing 737 was a major cause of that crash, which killed 78 people. The board has not yet ruled on what caused the Boston accident.

The circular also says that there is no way to predict how long anti-ice fluid sprayed on an airplane at the gate will prevent the buildup of new ice. Forty-nine minutes passed between the Air Florida jet's de-icing and takeoff.

"The bottom line is you've got to get out and look at the airplane" before taking off, Farrar said. " . . . It's the only way you can be sure that your airplane is going to be free of ice."

Federal aviation regulations prohibit pilots from taking off when "frost, snow, or ice is adhering to the wings, control surfaces or propellers of the aircraft."

However, other FAA documents say that take-off is permissible if a pilot is certain that any snow or ice will not adhere and will blow off as the plane gains speed on the runway.

The Air Florida jet's cockpit recorder indicates the crew expected the snow or ice on their plane to blow off. Some pilots say takeoffs in icy conditions are often conducted with that assumption.