This Margaret Heckler you wouldn't have recognized.

The other one, you remember, stood up there that October day beside the president, unsmiling and defiant, fighting back the tears as he told a skeptical White House press corps that his secretary of health and human services had agreed to leave the Cabinet to become U.S. ambassador to Ireland. It was post that was not, he emphasized, "a dumping ground."

This Margaret Heckler last night stood up there beside two former House colleagues, smiling and without rancor, fighting back the tears as they told a gathering of her friends that she had been responsible for starting "all this" -- "this" being the 8-year-old Congressional Women's Caucus.

"In her 16 years in the House and her three years in Health and Human Services, she has gone the extra mile for women, the disadvantaged, for veterans and Americans in need," said Rep. Olympia Snowe (R-Maine), cochair with Rep. Patricia Schroeder (D-Colo.) of the 125-member caucus, which today numbers 110 men in its ranks.

Organized by the research arm of the caucus, the early evening bipartisan salute at the Rayburn Building fell by coincidence on the day the Senate Foreign Relations Committee began hearings on Heckler's nomination as ambassador.

Half the women members of the caucus were there, and about a dozen of the men. There was stiff competition for Hill guests from President and Mrs. Reagan, who were giving their annual Congressional Christmas Party. 'Twas the season to be jolly, and any administration Scrooges were at the other end of Pennsylvania Avenue.

But there were a few realists.

"All of us have watched Margaret in this year and we've grown with her and all wished we could reach out and give her a hand. She never seemed to need it but you just wanted to give her a hug and squeeze and say fight on," said Schroeder in her tribute.

Heckler denied to a reporter earlier in the evening that there had been any fight -- in particular, with White House chief of staff Donald Regan, who reportedly engineered her dismissal from the Cabinet when she refused to hear his "signals" that he wanted her out.

"We're not discussing that," Heckler said last night. "I'm an ambassador. I've got to become more diplomatic."

And she was plenty of that. Going to Ireland was everything she might have hoped for. "A fascinating assignment . . . a good time . . . I've finished everything here -- I did my space age and technology, I had a major breast cancer conference," she raved on and on.

Then on to the speech.

"I'm very pleased that I'm the first American woman to be envoy to the People's Republic of [pause] to [pause] uh [pause] from the People's Republic of Massachusetts to the Republic of Ireland," she recouped.

Charging ahead valiantly, she talked of breaking "new frontiers" as the first woman to "a country like Ireland" and credited "the enlightened men" who gave her the opportunity.

"I suggest a toast to the enlightened man who made this career possible for me, President Reagan," she said, raising her champagne glass.

Certainly Reagan thought it was a great chance for Heckler, according to Sen. Orrin Hatch (R-Utah).

"When I finally chatted with the president, he said it could have been handled better, but being Irish himself, he thought what a wonderful opportunity for Margaret," said Hatch, who felt she had not gotten a square deal from the White House, "but ultimately she did because being ambassador to Ireland is something she's very excited about."

Hatch defended Heckler's managerial skills, which had been under fire in some quarters. "She was a great manager. I'm chair of the authorizing committee [Labor and Human Resources] that overviews Health and Human Services, so I worked with Margaret on a daily basis. If anybody ought to know, I ought to know, and I'm saying she did a terrific job."

Said Heckler of the criticism, "Are you kidding? What issues have gone wrong? Will you tell me? I pulled all the divisions within my department together."

Said Schroeder: "Caspar Weinberger's efficient and she isn't? I find that amazing. They hang on to the men forever. They throw the women overboard with great abandon."