ROYAL SISTERS

Queen Elizabeth II

And Princess Margaret

By Anne Edwards

Morrow. 415 pp. $22.95

THE YOUNGER of two sisters always has a tough time.

There are those too-tight hugs in babyhood. Later, the hand-me-down dresses. Throughout childhood the bulletins, as each bedtime approaches, on the plans of the Thing with Long Teeth -- the one that slithers out of the closet to coil under your bed when the lights go out. It's not pretty.

England's Princess Margaret was spared some of the usual indignities. Crawfie, Alah and the rest of the nursery staff who attended her and young Princess Elizabeth saw to that.

But she had her own Thing with Long Teeth.

"I'm three and you're four," her sister announced to her one day in 1933.

"No, you're not," countered the tot. "I'm three, you're seven."

But Elizabeth didn't mean years. She was talking about the line of succession to the English throne.

And as time passed, the Thing grew: After a temporary boost to three with the abdication of Uncle David and the accession of her father to the throne, Margaret, with each birth in the family, sank lower and lower in the royal order. Now, she's 11.

On the surface it was always Elizabeth who had the harder row to hoe. Royal Sisters, Anne Edwards' new book, makes that plain.

"Teach that child not to fidget," old Queen Mary, their grandmother, ordered Elizabeth's nanny practically from birth. The pockets on all her little dresses were sewn shut to prevent sloppy posture and unseemly collecting. By 17 months, she shook hands with adults correctly. By 3 years, she could stand still for long periods of time, answer a salute, accept the bows and curtsies of adults, do the white-gloved Royal Wave and, rewarded with a cookie, control her bladder for the entire length of any royal outing.

Margaret, four years younger, was quicker, more talented at everything from languages to music-making and refreshingly rebellious. At 6, two hours after being sent to her room for some mischief, she was recalled to the presence of her mother the queen.

"I'm sure you are good now, aren't you?" her mother asked.

"No, I'm naughty still," she reported. "And I'm going to go on being naughty."

She did so.

"Papa, do you sing 'God Save My Gracious Me?' " she saucily enquired at 11, as the king was reproving her for some unroyal behavior.

Even her rigid grandmother, Queen Mary, found her "so outrageously amusing that one can't help encouraging her."

She craved and got attention. Undoubtedly, her sister was kind, serious and sensitive far beyond her years. ("Oh, Crawfie . . . Ought we to play?" Elizabeth asked her governess, at age 9, when her grandfather died.) But throughout her life, Margaret's theme-tune has been those Second-Banana Blues.

At 7, she threw a tantrum because the train on the outfit she wore to her father's coronation was made one foot shorter than that of her sister.

"I was born too late," she howled at adolescence, as her sister was enjoying the pleasure of young womanhood.

And finally, at 25, she had to make the ultimate sacrifice. With the shameful example of her exiled Uncle David before her, she gave up Group Capt. Peter Townsend, the divorced war-hero she adored with all her soul -- "mindful of the Church's teaching that Christian marriage is indissoluble, and conscious of my duty to the Commonwealth."

To compound her tragedy, Townsend was plainly an infinitely more appealing figure than her sister's husband Prince Philip. He was gallant, selfless, modest, genuinely heroic and deeply in love with her.

In contrast, the worldly Philip, as Elizabeth's mother told members of her entourage at the time, was "advised by" his uncle Dickie Mountbatten throughout his courtship of the sheltered and innocent heiress to the throne of England, which began when she was 13 and he 18.

For although Philip was devilishly handsome and of so-called "royal blood," his future without a British royal connection would have loomed dark. The exiled Greek prince had peculiar relations, including some unsavory Germans. He had no university degree, no money, no treasures and no income beyond his extremely small Royal Navy lieutenant's paycheck.

When he finally became engaged to the future Queen of England, he moved into Kensington Palace with all his worldly belongings in two suitcases. He did not even, his shocked valet reported, possess "a pair of proper hairbrushes."

And while his affection for Elizabeth was doubtless genuine, had he failed with her, as a friend remarked, "He would have happily waited for her sister to grow up." SOME of Royal Sisters ploughs familiar ground -- but not all. Edwards offers some particularly riveting new insights into the character of Edward VIII (when Prince of Wales) plucked from the diaries of Sir Alan "Tommy" Lascelles, his private secretary.

As heir to the throne the prince flatly refused to leave Tanganyika as his father lay dying, despite a stream of urgent cables from the prime minister, wrote Lascelles.

"It's just some election dodge of old Baldwin's," he said.

"Sir," protested his secretary, "The King of England is dying, and if that means nothing to you, it means a great deal to us."

Wrote Lascelles, "He looked at me, went out without a word, and spent the remainder of the evening in the successful seduction of a Mrs. Barnes, wife of the local Commissioner. He told me so the next morning."

It emerges, too, that as Prince of Wales he had long been planning to abdicate, and to marry Wallis Simpson, as soon as his father died. He was shocked to discover that he was left no money at all in his father's will. He got the Crown, but no cash. Lascelles believed that in the long, long telephone conversation he held with Mrs. Simpson immediately after the will was read, the lovers agreed "to renounce their plans for a joint existence as private individuals and to see what they could make out of the Kingship, with the subsidiary prospect of the Queenship for her later on."

Royal Sisters is a mine of delights for royalty buffs. It's rich in the sort of juice about royal manners, habits, dress, decor and snobberies that send Americans into a feeding frenzy at the newsstand every time Princess Di appears on the cover of People.

As for the English -- well, they're hopeless. A survey a few years back showed that 65 percent of them -- including people like Alec Guinness and several fire-breathing Communists -- habitually dream of taking tea with their queen at "Buck House," which is what the royals, and the dreamers, and Anne Edwards, call Buckingham Palace.

I think that in future, as a gesture of younger-sister solidarity, I'll try to take my out-of-body self over to Margaret's place at teatime, instead. It's not so crowded.

Diana McLellan, the Washington editor of Washingtonian magazine, grew up as an English younger sister.