Look! There on the radar screen! Is it a locust? Is it a honeybee? No -- it's the B-2 "stealth" bomber.

The Air Force's top brass, plugging the embattled bat-winged bomber before skeptical members of Congress, yesterday offered the latest sales pitch: a chart comparing the size of objects, ranging from airplanes to birds to insects, as they appear on radar screens.

"I'm wondering where on this continuum the B-2 falls," asked a perplexed Sen. Albert Gore Jr. (D-Tenn.), after scanning the chart that was issued to members of the Senate Armed Services Committee's panel on strategic forces and nuclear deterrence. "Is it the insect category, the bird category or is it still in the aircraft category?"

"It is in the insect category," replied Gen. Larry D. Welch, Air Force chief of staff.

"Is it in the locust category or the butterfly category?" Gore pressed.

"I think we have carried it just as far as we can," Welch retorted.

"Now we are into the classified area?" Gore surmised.

"We may have already gotten there," interjected Air Force Secretary Donald B. Rice.

The unusual military show-and-tell was designed to prove that although the stealth bomber -- one of the most expensive and controversial of the Pentagon's new weapon programs -- is not invisible to Soviet radar screens, it would be as difficult to detect as small bugs. The Air Force officials who testified yesterday used the blue-winged locust, the honeybee (the tiny worker bee, not the larger drone or queen bees) and the alfalfa caterpillar butterfly as examples of natural phenomena that would look like stealth bombers on Soviet radar screens. In the term of art used in such matters, the Air Force said the stealth and the insects would have a similar "radar cross-section."

This was a contention that left at least one radar expert skeptical.

"This comparison does not really characterize the problem properly," said Ted Postol, professor of science, technology and national security policy at the Massachusetts Institute of Technology. "You can see swarms of insects {on radar}, but an individual insect seems improbable."

Postol and Air Force officials said radars are not normally used to spot birds and insects, but can be set to detect them under special conditions. Postol said the radar cross-sections of birds and insects are studied to improve understandings of radar interference.

"It's a pretty big insect," said Postol of the bomber. The Air Force now estimates the 75 bombers requested by Defense Secretary Richard B. Cheney will cost $62 billion -- more than $825 million per airplane.

Air Force officials noted yesterday that flight tests of the bomber against radar detection will not begin until later this year.

"We anticipate no problems in the B-2 meeting its low-observability requirements," said Rice, who told subcommittee chairman Sen. J. James Exon (D-Neb.), "You have my word, if that testing fails to demonstrate adequate low observability, I will ensure reconsideration of the program."