The faces, for the most part, were young and unlined, but the theme of yesterday's commencement at Washington's oldest women's college seemed mainly to be middle-aged women taking midlife chances.

"I was 40 before I knew what I wanted to do when I grew up," best-selling novelist Jean Auel told the 75 graduates of 111-year-old Mount Vernon College.

"What I wanted to do is write fiction, but I didn't know that until I started writing it, and I didn't start until I was 40."

Auel, whose tales of prehistoric cave dwellers have skyrocketed her into the publishing stratosphere, shared the tree-shaded podium with Sen. Barry Gold- water (R-Ariz.) and 42-year-old class valedictorian Irma Dobkin, a former Montgomery County public schoolteacher who decided to leave teaching after 18 years to go into business for herself.

Goldwater, whose late wife and two daughters had attended Mount Vernon, was warmly received as he spoke briefly and humorously about love rather than "that old hackneyed theme of politics that you hear too much about."

But it was Auel and Dobkin, women with grown children and new professions, who seemed to speak to the younger graduates' anxieties and hopes as they told personal stories of women and power, children and nurturing, men and sexism.

"As a younger woman I believed I could change the world," Dobkin told the graduates and their guests, who included her father, mother, two children and husband.

"It took about 20 years to realize that to change the world I had to begin with myself. I had to give up the delusion that happiness was equated with finding the right man, that security meant pleasing others."

Dobkin said in an interview that she decided to leave teaching and the public schools after deciding that her deep involvement in committees to combat sex discrimination would preclude promotions.

After learning that her high school mathematics was inadequate for architecture ("Girls were not encouraged to take classes in those areas then"), she majored in interior design and set up her own business.

"My desire to succeed in the world of private enterprise is one I share with most of you," she said. "It is my tribute to the new womanhood."

Auel, author of "Clan of the Cave Bear" and "Valley of the Horses," also urged the graduates to welcome change as she described how a woman who married at 18 and had five children by age 25 evolved into one of the all-time best-selling novelists.

The first printing of her latest novel, "The Mammoth Hunters," was an unprecedented 1.1 million copies.

At 25, caring for her children at her Portland, Ore., home while her husband worked for an electronics firm, Auel said, she turned her voracious appetite for reading to nonfiction and discovered Betty Friedan's "The Feminine Mystique."

"I was the generation Ms. Friedan spoke to in "The Feminine Mystique" and her book was the catalyst . . . . Her book convinced me I could be whatever I wanted to be," Auel said.

With only a high school degree, she began taking physics courses at night.

For the next decade she continued night classes while working at the electronics firm, rising from a clerical job to a management post.

After eventually earning a master's degree in business administration, Auel quit her job.

Then she sat down at her kitchen table one night nine years ago to "try to work out a strange idea that had been going through my mind that day."

"I've always loved to read," Auel concluded, "but I was 40 before I knew I wanted to write. Perhaps I'd been edging in that direction all along, but I couldn't have done it any sooner. I wasn't ready. I had too many skills I needed to acquire, too much knowledge I needed to learn, too much life I needed to live."