A radioactive package has been loaded on the TWA flight. Two men, armed with Geiger counter and ionization chamber, run up the loading ramp. They have about ten minutes to go over the cabin before passengers begin to board.

Sound a little too far-fetched for a spy thriller? More like an airline executive's answer to Airport? Actually these heros are graduate students at the School of Public Health, and they're working on a project sponsored by the Atomic Energy Commission and the Department of Transportation to determine the effectiveness of present rules for shipping radioactive materials.

Some radioactive materials used in medical diagnosis have extremely short half-lives. For example, Molybdenum-99, manufactured in the Boston area, loses half its effectiveness in 67 hours; its derivative, Technetium, has a half-life of only six hours.

Consequently, such radiopharmaceuticals are often shipped in the cargo compartments of passenger planes.

But don't trade in your Youth Fare card for a Metroliner ticket just yet.

Preliminary figures from the survey, which began Monday, indicate that it would take about a thousand flights with radiopharmaceuticals to accumulate the exposure you would get from one trip to the doctor for X-rays, according to Dr. Jacob Shapiro, radiological health and safety engineer to the University Health Services and director of the Logan Airport survey.

"I suspect we won't find much," Shapiro said, adding, "To the individual there's no hazard at these levels."

Students at Northwestern University are conducting a similar survey at Chicago's O'Hare Airport. O'Hare and Logan were chosen because of the large number of radioactive shipments originating at these two airports.

AEC spokesmen estimated yesterday that 150 to 200 radioactive packages leave Logan airport a day. About 300 planes depart from Logan daily.

Stewardess Scrutiny

The Harvard students plan to inspect about four planes a day, six days a week, during the four weeks of the survey. The cockpit and stewardess areas will receive extra scrutiny with the radiation detection devices, because of the higher exposure rates to which aircraft personnel are subject.

Douglas G. Smith, one of the student investigators, said yesterday that the airlines had cooperated with the survey so far and that in some cases they had speeded up loading to give the students more time for the inspections.