They talked turkey at the White House yesterday, politically and otherwise.

Politically, the king of the Belgians delivered a little lecture and just in case some of his North Atlantic Treaty Organization buddies were listening, he reminded them that within NATO "friendship cannot exist without solidarity."

Otherwise, in a lighter vein, the turkey talk focused on a large wild one, which dropped in shortly before the King arrived to take its lunch on the front lawn, while scores of passing tourists, a White House staff and TV camera crews looked on.

Even President Carter, who acknowledged the turkey's presence to the king during the arrival ceremony on the North Portico, sent word he didn't want a feather of that turkey's head harmed.

At the luncheon, in perfect English during toasts, the king alluded to more serious matters confronting the United States and promised that "our country does not ignore its friends."

A master perhaps at maintaining neutrality between bickering Flemings and Walloons at home, King Baudouin played no such role in Washington for his second day of public remarks in connection with Belgium's 150th anniversary.

"At present the United States suffers the consequences of a flagrant violation of international law. There is no doubt, Mr. President, that Belgium understands fully the importance of what is at stake and also knows where its duty lies," said the king.

For its part of the luncheon, the White House pulled out all the stops to entertain Baudouin and Queen Fabiola in the manner to which royalty is supposed to be accustomed.

Abandoning the routine round tables for 10, the White House set up, for the first time under the Carters, an E-shaped table seating 140.And for the first time under any president, according to White House Social Secretary Gretchen Poston, the table was set up in the East Room rather than the State Dining Room.

"What's more ceremonial than a grand table," said obviously pleased White House Curator Clement Conger.

The vermeil centerpiece was also historic, brought back from France by President James Monroe and usually displayed but seldom used.

A guest list drawn from government, business, labor and the media had an equally heavy representation from the museum and arts worlds.

Besides Frank Stella, considered by some to be America's foremost abstract painter, there was James Michener, profile historical novelist whose next work, due in January, will deal with South Africa -- "which means I'm a very brave man if not too bright," he cracked.

On the modern state of royalty, Michener decided that as a group today's crop does "rather better than one might have predicted -- more democratic governments [in Spain, Britain, Belgium and the Scandinavian countries] with normal restraints which makes it a little more palatable."

In Belgium's case, Michener continued, King Baudouin has been " a very mediating factor. He's had a particularly difficult job because of the break in the country between the Flemish and the French. And he's been very adroit in handling this."

Last in Washington during the Nixon administration (when they were also entertained at a luncheon), the Belgian royal couple's presence gave Carter the forum for some Pennsylvania primary point-making.

With "armed invasion threatening peace in southwest Asia, with terrorism a constant preoccupation of statesmen and leaders and people, with economic threats to the security and well-being of our peoples . . . let us realize much more vividly the value of amity, mutual support and cooperation," said the president.

His guests got a birdseye view of the Rose Garden (abloom with tulips, however) when they assembled for aperitifs on the West Terrace off the State Dining Room before going through the receiving line.

Perfectly dissected whle lobsters followed by medallions of veal were served on the Johnson china. And White House pastry chef Roland Mesnier masterminded pink hibiscus shells ot of spun sugar as cups for coconut ice cream.

Throughout lunch, the New York Harp Ensemble played background music. Afterwards, Amy Carter and five fellow-musicians entertained with a Suzuki violin concert of six selections.