The first thing Lynda Bird Johnson Robb did when she was appointed head of President Carter's Advisory Committee for Women was to call Bella Abzug, whom Carter had fired from the job.

"I want her help," said Robb later, with aplomb, as if it were the natural thing to do.

In fact, for Robb, the consummate political daughter of Lyndon and Lady Bird Johnson, it was the natural thing to do.

The appointment, announced Wednesday, came as a surprise to many - including Robb. President Carter personally offered her the job Monday in the Oval Office.

She is an unlikely feminist by most standards, although she had lobbied for passage of the Equal Rights Amendment among the back-slapping, oldboy legislators of the Virginia General Assembly. She attended the National Women's Conference in Houston.

"I want to be a bridge between some of the women who've been very active and some of those who haven't been identified as being involved," Robb said. The word from the president and from Sarag Weddington, his special assistant, was that Robb is a homemaker who perhaps could reach to homemakers who feel the women's movement is not really theirs.

Bella Abzug explodes at that notion.

"That's a lot of nonsense," said Abzug in a phone interview. "Six thousand women wrote to me when I was fired - women not getting equal pay, married women, poor widows, rural women - all talking about the need to have changes. They all said they realized that the president's economic program affected them. They said they came to realize the Advisory Committee was fighting for their economic needs and they wanted to know what they could do."

Abzug said the committee operates under the handicap of not being independent enough, but about Lynda Robb, Abzug said only, "I know Lynd, I'm very fond of her, and I wish her well."

If the committee members have any criticism of Robb, they have held their tongues. At the vice president's reception for the committee Wednesday night, Robb, in a white suit and a straw hat with little flowers, was described by one committee member as "a cross between Mary Poppins and Eleanor Roosevelt."

"She's got the background, the credentials, the contacts," said one new member of the committee. "Now let's see how she handles them."

Lynda Robb spent most of her teen years here in Washington, growing up in the intense public spotlight cast on her father's carrer in the Senate, the vice presidency, and later the presidency.

She and her sister Luci, whom she considers one of her closest friends, were under constant public scrutiny. Lynda Bird Johnson's dating relationship with actor George Hamilton was chronicled in every possible detail.

After her graduation from National Cathedral for Girls in 1962, she attended George Washington University and the university of Texas, from which she was graduated in 1966.

She was married in a grand White House ceremony in 1967, to Charles S. Robb, a Marine who was once a guard in the White House and who had later fought in Vietnam. Both Lynda and her mother Lady Bird, campaigned extensively for Robb in his successful candidacy for Virginia lieutenant governor in 1977.

On Thursday Robb slipped into the afternoon committee meeting so unobtrusively that some members didn't know she had arrived. She had spent the morning in Hopewell, Va., distributing books at schools for the "Reading Is Fundamental" program, for which she speaks several times a month. It has been her principal volunteer activity.

Robb plunged into the meeting, introducing herself and speaking up when she had a point to make or a question to ask. She was friendly with the other committee members. Her voice projects well, giving her a friendly command in conversations, of which she seems unaware.

She is intrigued by this observance, ("Really? You think I'm loud? When?")

She wore her shoulder-length hair pulled back in a tortoise-shell head-band, apparently having discarded the bouffnat style she wore when she was a White House bride. She wore a conservative dress and dark-rimmed glasses. With her pale, flawless skin, she looks younger than her 35 years.

When the subject turned to a North Carolina school's progress toward meeting guidelines for equal athletic programs, Robb leaned forward, grasping her pencil. "That's good," she said. "Let's find some other success stories like that one.One bad thing is that the women's movement has gotten a reputation for bitching - pardon me."

After the Thursday meeting, Robb soberly lugged home two notebooks full of committee information. "I obviously have a lot to learn," she said."I think this will take a lot of work."

"Some of those people on the committee are experts," she said later at her McLean home. "I don't have the experience in Hispanic problems or Indians affairs. I don't have the sort of experience that Majorie Bell Chambers [the acting chairwoman, now a vice-chair] has."

Robb does not have the best track record in the public eye. It is suggested that now she can handle being in the limelight.

"Well, I don't know about that," she says, and laughs.

In the past she has been known to be cool toward reporters, demanding and impatient - sometimes downright rude - on the campaign trail for her husband.

But last night, with a handful of phone messages from reporters collected by her daughters, 10-year-old Lucinda and 8-year-od Catherine, she sat right down to return the calls.

I'm still shy," she said. "I hate getting up in front of crowds. I love my privacy."

She said she wants to "unite the women's movement, not divide it." Once, she said, she took a course at the McLean Community Center for women getting back into the "main-stream." It taught such things as how to write a resume. Asked why she took it, she shrugged her shoulders and said, "because I was interested."

On the subject of what the power and status of being a Johnson daughter can do for her committee, she says only : "I hope I can use it to persuade people."

Among her friends is Joseph Califano, secretary of HEW , whose department the Advisory Committee is constantly scrutinizing.

"Of course it was a political appointment," Robb said of her job. "The president's a Democrat and I'm a Democrat. Beyond that, I don't know." CAPTION: Picture 1, Lynda Robb; by UPI; Picture 2, Lynda Bird Robb; by Fred Sweets - The Washington Post.