On the night before she was named by President Carter to head a blue-ribbon national women's committee, Bella Abzug was in New York City's Union Square co-sponsoring a "mass tribute" to executed traitors and atom spies Julius and Ethel Rosenberg - a bizarre juxtaposition that points to many troubles in the White House.

Abzug's presence in Union Square suggests the president's wife and daughter-in-law had good reason to doubt the wisdom of the appointment. As co-chairman of the new National Advisory Committee for Women, Abzug will not help the embattled Equal Rights Amendment (ERA), a cause to which the entire Carter family is firmly committed.

But beyond ERA, the Abzug appointment points to this hard fact of life: After 18 months on the job, the Carter team remains surprisingly naive and uniformed about national politics. What's more, the internal debate over Abzug reflects a larger, more important contest within the White House about how Jimmy Carter can best regain his former standing.

Abzug has lost three elections in New York in three years and is considered a plague on ERA less because of her aggressive personality than her extremist politics. Her co-sponsors of the Rosenberg "tribute" were aging warriors of the old left (John Abt, of the Ware underground communist group of the 1930s) and activists of the new left (David Dellinger of the Chicago Seven). Henry Winston, venerable national chairman of the Communist Party, delivered a major address.

"What's wrong with Bella attending a New York liberal rally?" asked one White House aide, improbably ushering John Abt and David Dellinger into "liberal" ranks. But those Carter staffers sophisticated enough to understand Abzug's impropriety found out too late to do anything about it. "Oh, no," moaned a senior Carter adviser, "did she really do that?"

The impact os such antics on middle-class America explained the First Lady's misgivings about the appointment, as related to the National Press Club: "I sometimes am concerned about the legislators in North Carolina and South Carolina and Florida where we need (ERA) votes. Can they identify (with Abzug)? Will it help the ERA pass?" Daughter-in-law Judy Carter, a doughty ERA campaigner, not only wondered but actually opposed the appointment.

Abzug was saved by an unlikely benefactor: Anne Wexler, the bright new star on the president's senior staff. Abzug has never disguised her contempt for the pragmatic political methods of Wexler as a Connecticut Democratic leader. Yer, Wexler convinced Mrs. Carter that Abzug's appointment will do more good than harm.

Why? Partly because Wexler feels Abzug deserves a reward for defending the president against Womens' Caucus attacks at the 1976 Democratic national convention. But mainly out of fear of reprisals. Ms. magazine editor Gloria Steinem, women's activist and Abzug's close friend, was persistent in demanding the job for Bella. Wexler determined that risking attack from the women's movement was not worth it.

To many sophisticated liberal politicians, Wexler greatly overestimated the influence on women of Abzug, even when allied with Steinem. "Bella brings you nothing in New York, nothing in the women's movement, nothing in liberal circles," one veteran Manhattan reform leader told us. "What she does is kill ERA for you."

But even if Abzug still exercised real influence among those constituency groups, some Carter aides feel Wexler was pushing the president down the wrong trail.

Wexler has been a most welcome and invigorating addtion to the White House staff - bringing political experience, competence and enthusiasm for Jimmy Carter. But her technique is "coalition-building" - putting together interest groups to generate support (which explains her concern about the women's bloc if Abzug were rebuffed). Old-line Carterites claim that was not how Jimmy won the Democratic presidential nomination and that is not the way to reclaim his former allure.

Wexler has been hard at work trying to mobilize a coalition of interest groups - consumerists, labor, small businessmen, women and others - in opposition to capital-gains tax reduction. Her critics on the White House staff admire her skill but would rather see the president somehow appealing to abroad popular sentiment for tax relief.

Herein lies the real importance of Bella Abzug's appointment. Her job is so unimportant that honoring the co-sponser of the Rosenberg tribute will not hurt anything more than the fading chances of ERA. It is the political tactics behind it that affect many other issues as President Carter seeks his political recovery.