Love is a many-splendored thing, but it can get awfully expensive.

For the last five days, 35-year-old Keith Ruff has been in town showering his former girlfriend, 20-year-old Karine Bolstein, with enough gifts to make the sultan of Oman look like Scrooge.

It all started when Ruff, an ex-stockbroker from Beverly Hills, proposed marriage. Bolstein said no. Now he's wearing his heart on his wallet, having already shelled out an estimated $10,000 in wooing costs.

First he filled her family's Northwest Washington home with thousands of fresh flowers. When that didn't work, he parked a limousine (complete with bar and television) outside her door.

"It's very flattering, but at the same time nerve-wracking," Bolstein said yesterday. "The house looks like a funeral parlor."

Consumed with desire, Ruff hired a Learjet to stand by at National Airport to whisk the lovers away to Europe.

"I'm 20 years old," she said. "I'm not in the mood to get married."

Then there were musicians sent to serenade her, hired clowns to entertain her, caterers to feed her and $200 worth of champagne and liqueurs for her father.

"It's crazy," said Arthur Bolstein, Labor Department attorney and father of the bashful non-bride. "My wife called the police but they said there was nothing they could do. After all, he wasn't threatening us. Now, we're laughing about it. My wife says we should ask him to start buying steaks."

Bolstein said boxes of expensive cigars and a five-pound wicker basket of exotic nuts arrived at his downtown office yesterday, the latest gifts from Ruff. "Apparently he won't take no for an answer."

"I won't stop trying," Ruff declared. "I believe in love."

He would like to hire someone to be his knight in shining armor. If that doesn't work, then maybe See SUITOR, D4, Col. 1 SUITOR, From D1 a Prince Charming for a day. Yesterday he was combing the city looking for a real glass slipper.

"The guy's possessed," said Ted Rodill of Custom Limousine. Rodill says Ruff hired him five days ago. "It's real fairy tale stuff. All he wants is for her to say yes."

But Karine Bolstein isn't budging. "I'm definitely still saying no," she sighed. "I'm not in love with him."

The couple may be having trouble communicating, however. "When she calls, I hang up. When I call, she hangs up," Ruff said from his room at the Washington Hilton.

Next, Ruff, who claims he's independently wealthy, says he wants to take out a full-page ad in The Washington Post proclaiming his love. The cost: $9,000. If that doesn't melt her heart, he's planning to hire protesters to picket the restaurant where she works with placards proclaiming his passion.

"If you love someone, you don't give up," he said yesterday.

Ruff said he met Bolstein last July at the Tysons Corner shoe store where she was working. "I fell in love," he said. They dated for a while, then broke up. He proposed marriage. She refused.

"She says she's too young," Ruff said yesterday.

"I am too young," she said. "I haven't even begun to live."

Can anything halt this labor of love? Ruff says he may decide to give up "when my piggy bank runs out of pennies."

Which may be sooner than he thinks. Says Karine Bolstein, "I'm not about to give in."

Arthur Bolstein: "The other day he sent a note saying to leave the porch light on. He'd be by at 1 a.m. to pick her up. It's like Casanova or Cyrano de Bergerac."

Or, more recently, The Great Gatsby . . . which begins with the inscription:

Then wear the gold hat, if that will move her;

If you can bounce high, bounce for her too,

Till she cry "Lover, gold-hatted, high-bouncing lover,

I must have you!"