With yesterday’s ouster of Carleton Fiorina as the chief executive of Hewlett-Packard Company, the number of female heads of Fortune 500 companies dropped 12.5% to seven from eight, and aspiring female CEOs all over America lost one of their most visible role models.

Ms. Fiorina’s ouster was particularly striking because she was in such a small group, said the senior director of research at Catalyst, a New York firm that tracks women’s workplace issues, Paulette Gerkovich. “Any shift one way or the other does create quite the impact,” she said.

HP yesterday announced that Ms. Fiorina was stepping down immediately, and that the CFO, Robert Wayman, will be interim CEO as the company searches for a new chief executive.

When Ms. Fiorina was named CEO of Hewlett-Packard in 1999, she was hailed in the press for having broken through the glass ceiling even as she denied one existed.

“I hope that we are at the point that we have figured out that there is not a glass ceiling,” said Ms. Fiorina at a news conference at the time. “My gender is interesting, but really not the story here.”

But Ms. Fiorina’s ascendancy in high-tech was clearly a gender story.

“It’s excellent finally to have a woman CEO of a Dow corporation,” wrote the New Yorker’s James Surowiecki for the online political magazine Slate.

In the interim, Ms. Fiorina failed to deliver the profits she promised and oversaw a 50% drop in the company’s share prices. (The stock closed yesterday at $21.53, with 102.4 million shares traded on the New York Stock Exchange.)

During Ms. Fiorina’s tenure at HP, she took on founding family members to push though the company’s 2002 $18.9 billion acquisition of Compaq. That fight ended with Walter Hewlett, son of the company’s co-founder, being ousted from the board of directors after he sued the company.

While Ms. Fiorina has been able to cut costs, she has not been able to turn the Compaq acquisition into market dominance. The only division among Compaq’s major product lines that holds an industry-leading position is its printer group.

As for America’s female executive ranks, they have seen consistent but slow growth during the last 10 years, said Ms. Gerkovich.

In 1995, 8.7% of corporate officers in Fortune 500 companies were women. In 2002, the last year for which Catalyst has statistics, 15.7% of Fortune 500 corporate officers were women.

Also, in 1995, 9.6% of Fortune 500 board members were women, and in 2003,13.6% of Fortune 500 board members were women.

The remaining female Fortune 500 CEOs are Mary Sammons, Rite Aid; Anne Mulcahy, Xerox; Patricia Russo, Lucent; Andrea Jung, Avon Products; S. Marce Fulle, Mirant; Eileen Scott, Pathmark Stores, and Marion Sandler, Gold West Financial Corporation.