The official and so-called "ladies" luncheon is being liberated in Washington - almost while nobody is looking.

Yesterday, at Grace Vance's Woodlawn Plantation luncheon for Hannelore Schmidt, wife of Chancellor Helmut Schmidt of the Federal Republic of Germany, the men outnumbered the women - 25 out of 48.

Monday, at Rosalynn Carter's White House luncheon for the Empress of Iran, five men - one of them a United States senator - dined with 15 women in the Blue Room.

"Whenever it's appropriate, or possible, Mrs. Carter likes to have a mix," said a White House aide to the First Lady, Coates Redmon. "God knows, there is no policy to exclude men."

"We try to invite persons who have similar areas of interest," said Rosalynn Carter's press secretary, Mary Hoyt. "We don't feel we have to weigh the guests by sex but by areas of interest."

Grace Vance, too, "likes a mixture of people, guests who have something in common with the guest of honor." said a spokesperson in the State Department's office of protocol.

"Something in common," apparently, is no longer limited to gender. At the White House Monday, joining Farah Diba and her hostess, were Minnesota Democrat Sen. Hubert H. Humphrey. Iranian Ambassador Ardeshir Zahedi, Assistant Secretary of State (for Educational and Cultural Affairs) Joseph Duffey, Librarian of Congress Daniel Boorstin and author Alex Haley.

Yesterday at Woodlawn, guests represented both the U.S. and West German governments but in addition, there were labor, industrial and cultural leaders who are traveling with Schmidt's official party.

"When the chancellor asked me to come along," said Gerd Muhr of Dusseldorf, vice-chairman of the German Trade Union Federation. "I said, 'Okay, I will go to the United States and tell as much as possible our position on the International Labor Organization (ILO) and the importance of the U.S. remaining a member.'"

Two years ago, Muhr said then-Secretary of State Henry Kissinger notified the ILO that the United States would withdraw from membership in 1977. "I feel the Carter administration is not fixed on that position, and I feel that now is our chance to urge against it," said Muhr.

The trade unionist's presence, like that of others in the Schmidt party, was at the request of the German embassy. It was what one State Department spokesperson called "a little unusual but it's up to the chancellor, who wanted them to accompany him."

If what they had in common with Hannelore Schmidt was West Germany, what others at the luncheon had in common was an interest in horiculture. Woodlawn's administrator, George M. Smith, and neighboring Mount Vernon horticulturist Robert Fisher took her on a guided tour of the platation's formal gardens where she recognized several plants, even though some are not be found in Europe.

Luncheon toasts were offered with raised glasses of California Zinfandel 1973. ("Sehr gut" was the rating of Wendelgard van Staden, wife of the German embassy luncheons henceforth will be mixed.") Grace Vance spoke from a prepared text and Henhelore Schmidt responded extemporageously.

"Now I understand the clime," said one German guest mopping his brow despite an air-conditioned dining room. "It's a warm welcome, a very warm welcome indeed."