Jean Peters, a 20th Century Fox contract player whose unpretentious beauty earned her leading roles in some of the top films of the late 1940's and early 50's before she abandoned her career and practically disappeared from view after a secretive marriage to the billionaire Howard Hughes, died on Oct. 13 at her home in Carlsbad, Calif. She was 73.

The cause was leukemia, The Associated Press reported.

Ms. Peters, who was known as Pete during her acting years, was a lead actress from the moment she arrived in Hollywood at the age of 21 after winning a Miss Ohio State beauty contest whose prizes included a Fox screen test.

The studio quickly offered her a seven-year contract. Within months of being driven cross-country by her widowed mother, the owner of a tourist camp outside their hometown, Canton, Ms. Peters was chosen as the female lead in the lavish epic ''Captain from Castille,'' opposite Tyrone Power.

Though never considered one of Hollywood's great actresses, the green-eyed, fresh-faced Ms. Peters had a straightforward naturalness on camera that made her a favorite leading lady of some of the top stars of the period.

She appeared with Ray Milland in the baseball comedy ''It Happens Every Spring'' (1949), and with Marlon Brando in Elia Kazan's ''Viva Zapata!'' (1952), Richard Widmark in Sam Fuller's ''Pickup on South Street'' (1953), Joseph Cotten and Marilyn Monroe in ''Niagara'' (1953), Spencer Tracy in ''Broken Lance'' (1954), Burt Lancaster in ''Apache'' (1954) and, perhaps most memorably, as one of three American women in Rome in Jean Negulesco's ''Three Coins in the Fountain'' (1954).

Many remarked at the time on Ms. Peters's informal off-camera style, avoiding Hollywood night life and the networking scene in the studio commissary for private picnics with her hairdresser and makeup artist on the floor of a dark set.

She was most often seen without makeup and wearing jeans and simple shirts. She lived in a rented bungalow decorated with watercolors she had painted herself. The studio publicity machine painted her as an Ohio farm girl and a bit of a tomboy baseball fan, an image that was difficult to reconcile with the sculptured beauty who appeared on the screen.

''Back home, I still have 3 dogs, 18 cats, a goat named Josephine and a lamb called Ali Baba,'' she told an interviewer in 1948.

To another, in 1949, she remarked: ''I don't like servants or big houses, and I'd hate to waste my time playing bridge in the afternoons. I think women need to cook and sew.''

Shortly after arriving in Hollywood, Ms. Peters met and began a quiet relationship with the reclusive Hughes -- also famous for his ostentatiously unpretentious wardrobe -- and for a decade the couple dated, usually getting together once a week, often to watch movies until late into the evening in one of Hughes's screening rooms. Among his holdings at the time were RKO Studios, Trans World Airlines, Hughes Aircraft and the Hughes Tool Company.

She was rarely seen in public and never in the company of another man, though Hughes was often seen on the town with some of the top actresses of the day. Because of the long nature of their relationship, there were frequent rumors that the couple had secretly wed.

For a few months, in 1954, Ms. Peters was married to Stanley W. Cramer 3rd, a Texas oil executive, but it ended in divorce and, like all of her marriages, without children. It was in 1957 that another rumor arose of a secret wedding between Hughes and Ms. Peters. This time it was true. The couple had married in a private ceremony in Tonapah, Nev.

Ms. Peters, whose final movie was ''A Man Called Peter'' (1955), retired from film acting and was rarely seen in public during the 13 years she remained married to Hughes. Neither granted interviews.

Over the years, Ms. Peters established herself in a remote, hilltop mansion in Bel Air while her husband, growing ever more reclusive and secretive, adjourned to the penthouses above a Las Vegas casino where he passed most of the last decades of his life.

They would still get together once a week or so, usually watching movies in Hughes's sanctuary.

An acquaintance, D. L. Lyons, a writer for The Ladies' Home Journal, described Ms. Peters's cloistered life in the late 1960's when he tried to visit her. ''At that time, in 1968, very much married to Howard, she lived in splendid solitude on Bel Air Road, atop a peak of the Santa Monica Mountains, under 24-hour surveillance of guards who followed her everywhere,'' he wrote.

By 1970, with her marriage disintegrating, Ms. Peters moved to a smaller house in Beverly Hills, let the guards go and even began to appear in public, attending movie screenings and going to restaurants.

Shortly after her divorce became final in 1971 she was married for a third time, to Stanley Hough, vice president and director for production operations at 20th Century Fox. Mr. Hough died in 1996, and Ms. Peters moved to be closer to her sister in Carlsbad, a suburb of San Diego.

According to reports at the time of her divorce from Hughes, Ms. Peters had agreed as part of the settlement not to discuss their private life together and not to return to movies, at least as long as the billionaire was alive.

In 1976, though, shortly after his death, Ms. Peters made her first screen appearances in two decades, playing roles in a television mini-series, ''Arthur Hailey's The Moneychangers,'' and in a public television production of ''Winesburg, Ohio.''

In 1981 she had a role in another television film, ''Peter and Paul.'' After that, she made only rare guest appearances on television series like ''Murder, She Wrote.''

A friend, Arlen Hurwitz, once recalled how Ms. Peters reacted to the attention of fans during the height of her career in the late 1940's. ''Whenever fans stop Jean on our wanderings, she has her own patented way of handling them,'' Ms. Hurwitz said.

''They say, 'Are you Jean Peters?' and she frowns and asks in a puzzled voice, 'Who is Jean Peters?' It always works. They go off looking bewildered and we go on about our business.''

Elizabeth J Hough