One hardly feels the presence of a Vanderbilt or Rockefeller, yet sitting here in a New York hotel suite are two of the four members of Sweden's largest corporation -- bigger than Saab or Volvo, better known than the films of Ingmar Bergman, hotter than saunas -- the rock group ABBA.

Bjorn Ulvaeus, who looks as much like a pop star as Hans Brinker, is doing a little mental calculating.

"I suppose," he says dryly, "that we've sold between 50 and 60 million records in four years." The numbers tumble out in detached digits.

For pop music superstars, Ulvaeus and his wife, Agnetha, are surprisingly friendly and outgoing -- and terribly normal. No TVs thrown out the windows into the swimming pool for these two. And no crowd scenes: They can walk around New York and not be noticed. When they check into hotels, they get asked for identification. This despite the fact that the group's net annual income reached $10.3 million by the end of 1977 -- and is expected to be much higher for 1978.

"8e are," says gnetha, "not -- what do you say -- a household word in this country."

It is just the opposite in Europe. "We got mobbed in a London pub," she says, "and had to rush back to the hotel. I couldn't do any shopping."

It boggles the mind to think that ABBA first performed less than five years ago at the 19th Annual Eurovision Song Festival Contest. They sang a ballad titled "Waterloo," and something clicked in the ears of the half-billion European TV viewers.

Since then the group has only rarely been off the European pop charts. They have far exceeded the sales of the Beatles in an equal time period (although, since 1964, the Fab Four have sold about 100 million discs).

Yet in this country, ABBA has mysteriously failed to achieve superstar status. Last year the group had its first No. 1 record here, the upbeat, discoish "Dancing Queen." It was a quintessential ABBA piece: strong female vocals, a bouncy bass line and thickly layered musical textures to carry the melody.

"We've got a different tradition," says Bjorn Ulvaeus, trying to explain the difference in popular reaction on two sides of the Atlantic. "Europe is very much into melodies, not into rock and blues to the extent you are here.

"And Europeans are, in general, more used to hearing female vocals. Then, you Americans always like to characterize music. I think ours blends pop and rock and jazz, with very much influence from the Beach Boys and the Beatles."

ABBA's music is highly distinctive, although to some Americans it seems homogenized. The sound is rich and polished, often slick enough to belie the bite of some of the lyrics (composed in English):

The songs you sing are too romantic

And when you want the truth

They only spit in your eye

They're only telling you lies

"I think maybe we're so popular," Bjorn Ulvaeus says, "because we're very ambitious and very determined. We work harder when it comes to writing and producing than most people do.

"In Europe we've been very successful with TV. It certainly seems like we can't reach people here with television [in addition to last week's UNICEF concert, which brought them here, they've been on "American Bandstand," "Don Kirshner's Rock Concert" and "Saturday Night Live"], which is why we will do an American tour in the fall. We've only done one major tour since we formed. Touring is very destructive and not very good for your creativity."

When ABBA was formed in 1974, Bjorn Ulvaeus was playing guitar in a folk group called the Hootenanny Singers, and Agnetha Ulvaeus was singing with a dance orchestra. Benny Andersson played keyboards in a rock group called the Hep Stars and Frida Lyngstad was a jazz vocalist. Andersson and Lyngstad were married last year. The group first met when each of them was asked independently to sing back-up vocals on a recording project.

Four years and five albums later, they were investing in real estate, an art gallery and an oil trading company.

"We don't take much out as personal income," Bjorn Ulvaeus says. "The personal income tax rate is 83 percent. The corporate tax laws are pretty good, and that's the only reason we've been able to stay in Sweden. We don't lead a flashy life.In Sweden, people tend to be very reserved."

"John Travolta could walk down the main street in Stockholm," says Agnetha Ulvaeus, "and nobody would go up to him."

Reserved indeed: As the Ulvaeuses chatted in New York last week, they seemed like a warm, happily married couple. A few days later a Swedish newspaper reported that they had decided six months ago to get divorced, although the group would remain together.

"We're the best of friends, just living in two separate homes," Bjorn Ulvaeus said yesterday by phone from Stockholm, confirming the report.

And why hadn't they mentioned their plans in New York?

"You didn't ask."