''What are these things called money, work, and sex?'' The pragmatic question was put to 6,000 couples by two University of Washington sociologists. The answers - 656 pages' worth, packed between the shiny silver covers of ''American Couples'' (New York: William Morrow & Co., $19.95) - are being generally accepted as the definitive word on relationships - married, cohabiting , gay, and lesbian. ''At last!'' the collective commentators seem to say. ''Now we know that 59 percent of wives and 39 percent of husbands are 'relationship-centered'; that 39 percent of wives believe they should work, but only 31 percent of husbands agree; that 32 percent of male cohabitors and 27 percent of female cohabitors favor pooling of funds.''
It hardly seems the kind of tallying Elizabeth Barrett Browning had in mind when she wrote, ''How do I love thee? Let me count the ways.''
''How do I relate to thee?'' might be the more appropriate question here. Researchers Philip Blumstein and Pepper Schwartz appear positively terrified of the word love, which appears only once on the entire 38-page questionnaire and only once in the index, for an entry labeled ''Love-sex segregation.''
Parts of the questionnaire, sponsored by a hefty $236,000 grant from the National Science Foundation, read like a print version of TV's ''Newlywed Game.'' As if from fear of being pretentious, the inquiry can become so trivial it almost disappears from sight, as in the sequence:
''How often do you and your partner perform these tasks together?
* Taking care of the yard.
* Doing the grocery shopping.''
Yet where's the humor in questions like: ''How would you describe yourself?
* Ambitious (scale of 1-10).
* 'Movie star' good-looking.''
And what's the point in questions like: ''Did either of your parents send you a Christmas or Channukah card last year?''
Does any couple really feel this is getting at the heart of love, or even their ''relationship''? Are we going to understand Romeo and Juliet by finding out who takes out the garbage? Or how they would spend an extra $600? More to the point, are we going to understand ourselves any better by applying statistical evidence to what is essentially a matter of the heart? There's a chill factor here that can't be disguised merely by defining this as ''scientific research.''
''We have become a nation of statistics-watchers,'' warn economist William Alonso and sociologist Paul Starr of Harvard in a paper prepared for a conference on the census. ''Statistics are commonly presented and accepted as neutral observations, like a weatherman's report on the day's temperature and atmospheric pressure.''
After eight years, 175,000 computer cards, and 75 file drawers of information , Mr. Blumstein and Mrs. Schwartz rather cautiously express the hope that their findings will help couples ''identify roles.'' But they do not dare allow even this timid banality to stand unqualified. ''Each couple,'' they hastily add, ''will have to establish guidelines. . . .'' Love's labors - or rather relationship's labors - seem to be lost. After all those pages, a reader is back in the unplotted wilderness with no map and a hundred paths to choose from.
The week following the much-heralded publication of ''American Couples,'' another book on the subject quietly took its place on bookstore shelves: ''Giving Time a Chance: The Secret of a Lasting Marriage'' (New York: M. Evans & Co., $13.95). Here there's not a computer card in sight. No statistics, charts, or graphs, and no assumption of scientific authority. Just two Michigan friends, Ronna Romney and Beppie Harrison, examining the particular qualities that make a relationship - or rather, love - work and last.
Here the famous (Olivia and Jack Anderson, Mary and Lee Iacocco, fashion designers Pearl and Albert Nipon) and the not-famous (''Marcia and David,'' ''Helen and Joe,'' ''Jenny and Ralph'') talk about their marriages - the challenges and rewards, the good times and the bad. There isn't a couple in the book who hasn't ''hit a bad patch'' - often many of them.
''There are times in every marriage when it seems it would be a lot simpler just to walk out,'' the authors conclude. ''The strength of the long-term marriage is not that those times don't happen: It's that nobody walks.''
''A marriage,'' they continue, ''is an entirely individual construction built by two unique people, and it is built with their love and their happiness and their exasperation and their tears.''
This is a book disarming in its candor and in its eloquent comments about what marriage is - and isn't.
''There is no end to human ingenuity in working out ways for men and women to get along together,'' the authors sum up simply.
How the fashions change! Ten years ago the talk shows were buzzing with the soon-forgotten thesis of ''open marriage.'' Now, except for the perennial private observers like Romney and Harrison, love has been taken over by the statisticians - those who avoid all advice in favor of reporting the Dow Jones averages of the heart.
''The horizon has not remained the same,'' the philosopher Denis de Rougemont conceded 45 years ago in ''Love in the Western World.'' But then he extended that horizon to include what it must include: a sense of mystery, a sense of the sacred. He wrote to those troubled in their marriages then: ''A fidelity maintained in the name of what does not change as we change will gradually disclose some of its mystery: beyond tragedy another happiness waits.''