Eleanor Lansing Dulles celebrated her 90th birthday yesterday with the shortest lecture ever heard in this capital of endless mutter, scream and sermon.

"I have this long lecture to deliver to you," she said, rising from her grand armchair on the lawn, "so you may as well lean against each other while I deliver it."

Her pale eyes sparkled and she said, "Thank you. Thank you all."

The 200 guests, standing about with enormous glasses of champagne, responded with gratitude and jubilation to the woman who in 60 years of public life has lectured, written, performed as economist, social critic and mover in foreign affairs as well.

Messages congratulating her arrived from the secretary of state, the chancellors of West Germany and Austria, three former mayors of Berlin and the like.

"In the 1950s," said Jack Button, then a consul and now retired, "East Germans were streaming across the border, and Eleanor turned Washington around overnight -- she ran what amounted to the Berlin Desk then -- and got food and necessities for them. She wanted them well treated and saw to it they were."

She recently returned from West Germany -- her dinner partners there were lustrous types like Willy Brandt (chairman of the presidium of the Social Democratic Party) and she sat at head tables in various baroque palaces and was made much of for her work years ago to re-establish German-American relations.

Since hardly anybody is now alive who remembers World War II, there were even fewer who remembered her work getting Social Security established in the 1930s. She was never a household name like her brothers, the late John Foster Dulles, secretary of state, and Allen Dulles, Central Intelligence Agency chief, but she did important work, not necessarily dazzling the public eye. Many at her birthday reception were wheel horses in the State Department, Brookings Institution, various other government agencies, and consultants.

If you didn't already know her you had no idea she was the woman in the white dress embroidered all over with roses, since she chatted with groups in white chairs and walked about talking with men standing up eating shrimp. She was always something of an athlete. She swam the Rhine and, it was said, she never saw an ocean without swimming more or less across it, so that even now her handshake is quite firm, her gaze surprisingly direct, and her absence of small talk and falderal almost total.

Back of her was a charming wood house painted yellow with green shutters, and before her were terraced manicured lawns with box bushes, black squirrels and a great catalpa tree in full bloom -- headquarters of Youth for Understanding, a student exchange organization in Cleveland Park. She has always concerned herself with the young and with education. Her book, "Chances of a Lifetime," is a classic Washington memoir treating many fields of interest.

Her cousin, Francis Allen (one of the few New Dealers around) and Ambassador Jonathan Dean led the toasts after some thin-ice comments on Eleanor Dulles' near-century of lively arguments with one and all -- "the odd thing was she also listened to other arguments than her own and digested them carefully," as one of her intimates said.

James C. Williams, a young man and an old friend, recently took off a couple of weeks from the Commerce Department to accompany her to Germany, and said of the general feting that several times he actually got a little sleep.

"And I imagine you saw to it people did not push and bump into her," a man said.

"And saw to it she did not push and bump into them," he said, because Eleanor Dulles (after her husband's death a half-century ago she resumed her maiden name) is not one to just sit on the fringes like a china shepherdess.

Asked how she thought Social Security had developed in the decades since she worked in the establishment of it, she looked the questioner straight in the eye, decided she was not going to spend her birthday party on political arguments, and said:

"They changed it."