"I've been told this is all off the record and the cameras are off," President Reagan told the black-tie crowd at the White House News Photographers Association dinner last night. ". . . I've been waiting years to do this."

Then the president of the United States, before 1,000 guests, stuck his thumbs in his ears, fingers spread-eagled from the palms and wiggled them clown-fashion.

He did it so quickly, so slickly (he must have practiced for hours in front of a White House mirror), that by the time the laughter at the Sheraton Washington Hotel ballroom rose to a full roar, his hands were back on the podium and he was simply standing there with a satisfied grin.

Tuxedoed photographers, at their own party but some still wise enough to have the tools of their trade with them, clumped in front of Reagan with cameras poised. "Do it again," they urged. But too late.

Too late? Who's kidding whom? Someone, of course, got the picture. In fact, C-Span, a cable TV network, was broadcasting the dinner live. And at least one news service sent the picture out over its photo wires.

Asked later if the president knew he was being televised, a White House spokesman said: "Sure, of course."

"I like photographers," Reagan said in his remarks. "You don't ask questions. Can you imagine Sam Donaldson with a camera? The thought, as you say, makes me shutter."

Groans all around.

"I've been told there's a feeling among photographers that journalists don't treat you well enough," Reagan said. "Welcome to the club."

Reagan couldn't resist a few partisan tweaks, either: "You have wide-angle lenses wide enough to get all the Democratic presidential candidates in," he said to laughter. "You just don't have lenses wide enough to get all their promises in." The room swelled with ominous "ooohs."

The president also lobbed a shot at the print media. "If the written or broadcast media could capture the truth as accurately and consistently as you do, the American people might have a better perspective on many issues of the day."

But some photographers were still talking of The Picture. "Whoever got that picture gets the presidential award next year," sighed one photographer, referring to a prize the photographers give annually. After all, this group had made reputations and won awards capturing startling and fleeting moments sometimes before they even knew they had the moments.

For example, there's George Fridrich, an NBC cameraman, who was named television photographer of the year by the association. Several years ago, he was covering President Ford leaving a routine event in San Francisco, walking to his limousine.

"I was doing my job. I wasn't doing anything special," Fridrich said. "As he gets in the car--you always widen out to get him going into the car, then zoom in on the crowd--there's a bullet shot, I widen out, then I zoom in and get the agents holding Sara Jane Moore."

In this case, he not only hopped into a car in the motorcade whisking Ford to the airport--"in a shoot-out you have certain procedures you follow"--but his producer also hopped in a car, and when they arrived at the airport, they flagged down a woman in a Volkswagen, paid her $50 to take them to the local NBC affiliate, "and NBC got on the air with it first," Fridrich said.

Then there's AP photographer Dennis Cook's shot, an award-winner this year, of Speaker of the House Tip O'Neill, Senate Majority Leader Howard Baker and Reagan sitting scrunched together at a reception. Baker and Reagan are yukking it up while O'Neill on the far left stares off glumly into space.

"I don't know what they were talking about," Cook chuckled last night. "I was just trying to get them all into the picture with the Capitol in the background. The expressions on their faces were extra."

Earlier in the evening, while guests munched on hors d'oeuvres at a reception, some of the award-winning moments that cameras of guests in the room had seized flashed on giant screens: A Palestinian child with a kitten tucked in the crook of his elbow. Maya Ying Lin looking like the Mona Lisa. Bruce Dale's almost surreal color photo of a woman swimming through crystal Bahamanian waters toward the camera.

"Probably the most exciting pictures are the ones I shot yesterday," said Dale, a National Geographic photographer, who just returned from Key West, Fla. "Visualize this: a long line of sky, a long line of ocean and 20 to 25 preschoolers sitting on a wall in their bathing suits waiting to drink out of a gallon container of milk . . . The picture I won for here was as planned as anything. It's a nice picture, but not as exciting as discovering 20 kids on a wall."