BOOK REVIEW / BIOGRAPHY : A Vibrant Tribute to an Enchanting Lady : AMERICAN EMPRESS: The Life and Times of Marjorie Merriweather Post <i> by Nancy Rubin</i> ; Villard $27.50, 445 pages Illustrated

When Marjorie Merriweather Post reopened her Palm Beach estate, Mar-a-Lago, in the winter of 1969, her return was heralded with the newspaper headline “The queen is back--long live the queen.” Her admiring biographer has elevated Post to empress, and the promotion seems well-deserved.

Nancy Rubin’s subject was truly regal; lavishly philanthropic, remarkably astute in business affairs, politically sophisticated, gracious, considerate and stunningly beautiful; a woman of multiple accomplishments who thoroughly merits the attention and affection Rubin has accorded her.

The biography is not only a tribute to one of the century’s great ladies, but a fascinating social history of American life from 1887, when Marjorie Post was born, to 1973, when she died at the age of 86.

Marjorie Merriweather Post was the heiress to a fortune that began when her disabled father journeyed to Battle Creek, Mich., in the hope that Dr. Kellogg’s strict regimen would cure him of an assortment of incapacitating symptoms.

Once recovered, C. W. Post decided that the burgeoning health-food industry needed a hot drink of roaster grains and sweeteners to replace coffee, forbidden at the Battle Creek Sanitarium. Post achieved a surprisingly palatable mix of wheat berries, bran and molasses.

The result was Postum, and soon a dyspeptic, nervous nation was demanding it, interest roused by Post’s innovative marketing techniques. The entrepreneur overcame his reluctance to rival the man who inspired (and cured) him, and the Postum Company soon diversified to include breakfast cereals.

C. W. Post settled in Battle Creek, and his only child grew up with solid Midwestern values in the health-food capital of the world.

Though she would eventually--and often simultaneously--own a 360-foot sailing yacht, a 115-room Palm Beach palazzo, a 200-acre Adirondack camp staffed, in season, by 85 loyal retainers, a 54-room Manhattan triplex apartment and equally grand establishments on Long Island and near Washington, the lofty moral standards, the altruism, and the sound common sense instilled by her father never deserted her.

Celebrated as a hostess, revered for her charities, admired for her beauty, taste, and charm, she remained, according to her biographer’s account, a kind, friendly, and altogether enchanting person, conscious of her good fortune and acutely aware of the many obligations such blessings imposed.

She was unlucky only in love. An incurable romantic, she was married four times. Her first husband was Edward Bennett Close, a somewhat ill-considered match apparently prompted by her bereaved father’s wedding to the woman who had been Marjorie’s governess.

Contracted in 1905, the marriage to Close was a casualty of World War I--a case of Marjorie and Ed growing apart during his absence.

Close was succeeded by the financier E. F. Hutton, an apparently blissful union destroyed when Marjorie discovered his many infidelities.

Her third husband was Joseph Davies, the worldly, intellectual Washingtonian who became Franklin D. Roosevelt’s ambassador to Russia, an assignment that provided his wife with some of her most rewarding and challenging adventures.

Advancing age and illness sadly altered Davies’ personality, turning him into a tyrant, and regretfully, Marjorie divorced him in 1955, resuming her maiden name.

Three years later, at the age of 71, she was married for the fourth and last time to a Pittsburgh businessman named Herbert May, a romance that ended abruptly when evidence of May’s homosexuality arrived in the mail, horrifying his fond wife, who had no inkling of what many others in her circle had known all along.

Divorce, however, seems to have been the only shadow in an otherwise exemplary life.

Despite the anguish these failed marriages must have caused her, Marjorie Merriweather Post never allowed her emotional problems to interfere with her good works or the shining face she showed to the world.

Rubin treats her subject’s personal life with discretion, emphasizing her sterling qualities: the vision that led her to acquire the Birdseye frozen foods company, the versatility she displayed as an ambassador’s wife in the Soviet Union, her unfailing generosity, her roles as wife, mother and public figure.

Resilient, optimistic, and marvelously genuine, Marjorie Merriweather Post seems entitled to every accolade in this vibrant and thoughtful biography.