This could be one reason why President Reagan looked, well, different, when he and Walter Mondale went at it in the first of their two televised debates: Maybe, just maybe, the president hadn't eaten his daily pick-me-up of bee pollen.

A devotee ever since author Marjorie ("The Golden Pollen") McCormick of Yakima, Wash., sent him some in 1961, Reagan devours bee pollen bars the way other people eat jellybeans. Air Force One keeps a supply of both on board as does Executive One, the C9 jet that flies Nancy Reagan around the country. When it runs short of bee pollen bars, stewards have been known to make frantic calls to the Scottsdale, Ariz., firm that makes them.

"They're great for taking the edge off your appetite when you're hungry," says Mrs. Reagan, who, with the president, once recommended the bars, with their calorie count of 153, to Maureen Reagan and her husband, Dennis Revell. "They said, 'You eat these things because you really like them?' "

Sold in health food stores under the label "The President's Lunch," the White House buys them by the case from C.C. Pollen Co. This brand, which was first made last year, was introduced in Japan when Reagan made a state visit there in November.

Already named for his office, Reagan, with Prime Minister Yasuhiro Nakasone, gave the bars the plug of gold by eating them on television at a lunch Nakasone was hosting. Talking about their favorite foods, Nakasone said he was crazy about beans and Reagan confessed that he always has a hankering for bee pollen bars.

Finnish athlete and bee pollen aficionado Lasse Viren started the rush among athletes for the golden elixir after running off with the 5,000- and 10,000-meter races in Munich in 1972 and repeating his performance in 1976. Among politicians, who also run a lot, Reagan's preference predates that by more than a decade.

"I was plowing one of our California ranch paddocks and late in the afternoon realized I had one of the bars you'd sent in my jacket pocket," Reagan told McCormick in a handwritten thank-you letter dated Dec. 10, 1961. "I ate it and I swear it is not my imagination but twenty minutes or so later I was definitely conscious that I was no longer fatigued and the chill I'd been feeling was gone."

Nikki Antol, marketing vice president of the Scottsdale firm, says that besides combating fatigue, bee pollen has rejuvenating effects, a claim that ought to make converts out of Mondale Democrats as well as Reagan Republicans. She is sure, for example, that Reagan's 23-year pollen diet is "the secret of his natural hair color."

Elaine Crispen, Nancy Reagan's secretary, didn't laugh when Antol suggested that C.C. Pollen Co. use the endorsement "By appointment to President Reagan." But White House aides are accustomed to queries about Reagan's fondness for bee pollen. For an article on pollen in the current National Geographic, writer Cathy Newman sent Reagan some bars she had acquired in the pursuit of her story.

In a letter following up her gift a few weeks later, Newman asked if Reagan was now able "to clear tall buildings at a single leap and race faster than a locomotive? More importantly, will bee pollen bars replace the jellybean as the Presidential snack?"

The White House thanked her for her gift but was politically noncommital on his ability to clear tall buildings in a single leap.

Also left up in the air was the status of jellybeans.