That ravishing Danish waitress who served you a frothy Kronenbourg at Tivoli Gardens last summer, can be your next wife. The distinguished Toyota VP you left on the Love Boat Cruise to Borneo can be your next husband.

Only a fiance visa stands between you and the altar.

Winning approval to marry a Swede can take less than a week, while a fiance petition for New Delhi may take as long as four months. In America, Indians take longer to marry than Swedes.

Marrying a U.S. citizen is perhaps the surest way for the foreign-born to forever remain in America, a land of blissful opportunity to the 115, thousands of aliens who request permanent residency by virtue of their marriages to Americans.

The Americans must promise the Immigration and Naturalization Service he's free to marry. The cable goes out to an American consult nearest the phone. He or she is summoned forth, and presto - WHOMP! - the stamp goes on the passport, good for 90 days, or until the wedding, when the foreign-born becomes eligible to stick around for good.

The plans of Roger Smith, 27, a rare-book dealer from England, haven't progressed that far. First, he'll walk down the aisle on April 15 in Swarthmore, Pa., with Jeanne Dangerfield, 27, a Washington, D.C., policy consultant. They met at a party and one week later decided to marry. They've been miserable ever since.

For one thing, Roger's tourist visa expired after he returned to London to pack, and the only way for him to return to the U.S. legally was by way of the "fiance," or "K" visa. It is a pseudo-contract that allows an alien to enter the U.S. as a non-immigrant excluded from various country quotas. Preferably, it is one with love, though affection is not a stipulation. Only honorable intentions are required: that the couple intends to marry within 90 days.

Last week, Dangerfield was told by government officials that processing her petition for a fiance visa could take upwards of three months.

But, she pleaded, the wedding was only two months away. The caterer had already ordered prime ribs for a reception at a Swarthmore country club. Invitations to 140 friends were ready for the nails.

Dangerfield nagged immigration officials, sought the aid of her representative, called her senator, kvetched to the State Department to speed up its handing of the fiance visa on the London end and generally made herself a nuisance.

Dangerfield even sent off a letter to her country's envoy to The Court of St. Jame's, Kingman Brewster, in hopes he might remember meeting her one summer 11 years back at Martha's Vineyard, where she played with his daughter. "I was desperate," she sighed.

One State Department official begged, "Please don't call over here any more. Roger will get his visa in record time." Which should happen today, St. Valentine's Day, when he is expected to stride into the American embassyin London, and sit for a brief interview with a consular official, a customary procedure.

In 1970, the first year fiance visas were issued to save the American the round-trip cost of traveling abroad to marry, the INS approved 64. Since then, about 5,000 to 8,000 couples a year have used the fiance visa to meet the exigencies of love.

As far as immigration officials can tell, most of the 115,348 aliens who asked to remain in the U.S. permanently after marrying Americans last year considered their matrimony serious. For others, marriage was mere convenience - less risky than, say, running the border at night, dodging Texas Rangers, prickly cacti and rattlesnakes, then praying all the way to Abilene, attached to the oil-soaked underbelly of a pickup truck.

Last year, immigration officials challenged 36,000 couples to please step into immigraztion offices to certify Cupid's aim is order to get their "green cards." The examiners denied 12 percent of interviewed applicants on the basis of fraud.They found such violations as fake birth certificates, forged divorce papers and almost 2,000 cases of marriage for money.

No statistics exist on how many couples married one day, applied for the "green card" and divorced the next. "Investigating fraudulent marriages," says one immigration official, "only began in earnest in 1976. But in the case of fiances, there's just no way to tell how many are in it for true love and how many are in it for citizenship."

Embassy officials assigned to interviewing finances abroad say they sometimes feel like stern fathers inquiring after the good intentions of a future son-in-law or daugher-in-law. Lyle van Ravensway, chief of the telephone inquiries branch of the State Department's visa office, interviewed 250 fiances during four years a s a consular official in Rotterdam. Many were Dutch women who got engaged to American airmen just before their transfer from a nearby NATO base. The fiance visa was ued to reunite them, during his efforts to consumate the process, Van Ravensway sometimes bumped into a few skeletons.

Police checks turned up a few records of prostitution, which disqualified the fiance. Often, the American was unaware of such history. Officials tried to gently break the news. "If he still wanted to go through with it, there was a complicated system of waivers," he says. "But i never had a case where the American fiance changed his mind."

The New York widow met Phillip Bridgeton, an Irish widower, on her package tour to the Emerald Isle. It was not a cheap trip, but, apparently, meeting Bridgeton (a pseudonym) made the trip worth the price.

Upon her return to New York, she went to the district INS office, and wrote Bridgeton's birth date and other statistics on the pink form, filled in her personals, marked the "Widowed" box and waited. And waited. And waited.

She called immigration, the State Department, her senator.Word was broken gently. The consul had phoned Bridgeton when the petition arrived. He was surprised. He didn't recall ever meeting her.

"How can we tell if it's true love?" asks Joe Mongiello, director of the INS Washington, D.C., district office. "We can't. But we're not the ones to determine if one fiance loves the other. If they break up, it's okay. Divorce is a common thing these days. There's no requirement in the petition for a fiance visa that says the marriage has to last, just that the couple intends to engage in a normal marriage within 90 days.

"Now, if I had to swear to you the day I married my wife, it was true love, I don't know if I could do it. We don't try to delve into the bedroom. We just process the paperwork."

There are romantic, epics with happy endings that would please Barbara cartland, and real short love stories - said affairs - that would crack the hardest heart.

Twenty-three years with the INS, John Bostrum has become expert at detecting the look of love. A former immigration examiner who has interviewed hundreds of couples, he now supervises other examiners at the INS district office in San Diego, which romance from across the Mexican border, as well as from Navy men who have fallen prey to Sirens on distant shores.

Bostrum meets the couples after the wedding, when they request the green card. "Anybody can hold hands and lean on someone's shoulder without being in love," he says. "But you get a sixth sense; you can usually tell if their intentions are bonafide within a couple of minutes."

The American finance, though, is not always as discerning. Just last week, two seamen fresh off a cruise to the South Pacific filed a fiance petition for the same woman, presumably left pining away in Manila. "I don't know which one turned out to be the lucky dog," laughs Bostrum.

Margaret Warren, a contact representative for the INS, works on the second floor of the district office at 1025 Vermont Ave. NW, where she was found smoking Newports and sipping a Coke on a break from the non-stop faces that line up at the window from 8:30 a.m. to 4 p.m., Monday through Friday. The office handles 15 to 20 fiance visa applications a month.

She runs into all kinds of amorous entanglemnts, and often feels like Abigail Van Buren. Just last week, a divorcee who had filed a fiance visa application to import her Venezuelan boy friend changed her mind. She had reconciled with her husband. So she dropped by to cancel the petition. A "Dear John" cable immediately was dispatched to the American consul in Caracas who, n turn, informed the fiance she no longer wanted to marry him.

"She was a little nervous," said Warren. She didn't want this guy showing up in the U.S. all of a sudden."