IN 1968, BEFORE establishing her national reputation, Elizabeth Drew produced for The Atlantic a classic account of Washington insiders and how they operate. Under an arresting title - "The Health Syndicate: Washington's Noble Conspirators" - her article recounted in startling detail how philantropist Mary Lasker, her lobbyists and her coterie of celebrity doctors coaxed, cajoled and even frightened members of Congress into voting huge sums for needed health research.

"The Health Syndicate" raised serious questions about national priorities and about policy-making on Capitol Hill. It raised serious questions about "special interest groups" that many journalists ignore simply because such coalitions seek no obvious form of self-enrichment. But for all these serious questions, the article would have flopped had it not been colorfully - even hilariously - written. No one, it seemed, understood better than Drew the optimum balance between informing readers and entertaining them. (She must have known she'd have a hit when she induced Mike Gorman, Lasker's flamboyant D.C. representative, to proclaim defensively, "We're not second-story burglars; we go right in the front door.")

Ten years after that triumph, in the summer of 1978, Drew set about producing a very different account of Washington insiders and how they operate. She spent day after day with Senator John C. Culver, an Iowa Democrat, watching intently as he plotted legislative strategy with his aides, took a whirlwind trip home to mingle with constituents, and grabbed a rare Sunday with his family to wander the banks of the Mississippi River. Drew's intimate glimpse of Culver's daily routine appeared first as articles in The New Yorker; those articles became this book.

Other writers have chronicled the days of other senators, but the combination of Drew and Culver represents a formidable pairing of journalistic and political heavyweights. In the years since 1968, Drew has served as Washington editor of The Atlantic, hosted a respected television series, probed candidates Carter and Ford during the presidential debates, and written highly-acclaimed accounts of the Watergate years and the 1976 presidential campaign.

Culver, for his part, has managed in a single term to become one of the Senate's most effective members. And for this type of book, he makes an ideal subject: articulate, self-aware, yet remarkably unselfconscious in Drew's presence, Culver shares much and appears to hide nothing. The constant companionship of a journalist would distort the behavior of most politicians, thus frustrating the journalist's purpose, but a sense of mutual trust seems to pervade the Drew-Culver relationship, permitting authenticity in a narrative form that depends on it.

In Senator, as in her books, Drew relies on the technique of recording observed events chronologically, in an unadorned and detached manner. This lets her points emerge inferentially, as impressions, rather than requiring them to be declared as bold conclusions. The accompanying prose is cool, even, almost flat; deliberately stripped of metaphor and powerful passages, her writing derives its force solely from her discrimination in selecting those encounters and remarks she chooses to record.

This risky - and presumably demanding - literary style serves Drew well in helping inform her readers. She does not need to assert that Culver is overworked, or a wily tactician, or deeply committed to his role as a legislative mediator: she can show us instead. When, near the close of any normal person's day, Culver surveys his remaining tasks and complains, "Doesn't it all just defy belief?", we are well prepared to say amen, having vicariously experienced the demands and the tedium of Senate life. (This is the book to read if you're wondering why so many members of Congress are declining to seek reelection.)

The troubling question, however, is whether Drew's literary style is wholly suited to this particular subject matter; does it contribute to, or detract from, her special ability to entertain as well as to inform? Part of the reason Drew's techniques worked so well in her Watergate book (Washington Journal: The Events of 1973-1974 ) is that the circumstances described were so dramatic, and their progression so well known. Reading Drew's Watergate chronicle, we reimmerse ourselves in the fascination of an era we experienced; Drew's power lies in evoking and recapturing our own past feelings of foreboding or astonishment.

The impact of Drew's account of the presidential campaign (American Journal: The Events of 1976 ) seems less than that of her Watergate saga precisely because the election lacked the drama of the scandal, and because it lacked a relentless momentum of its own. Senator, in this sense, gets even less help from outside forces: most readers lack a store of Senate memories to supplement the details suggested by stark prose, and part of Drew's purpose is to show Senate life not as dramatic, but as plain hard work. In these circumstances, there's a danger - to which Senator never quite succumbs - of relying on understatement and simple prose: the reader may starve for lack of stimulation.

Fortunately, Senator signals only the limit of a particular literary technique, not the ossification of Drew's talent. In a recent New Yorker, Drew has written a lively profile of Carter confidant Robert Strauss, telling us what she thinks, as well as what she saw and heard. The Strauss article heralds the return of the special qualities that "The Health Syndicate" displayed a decade ago: color, snappy prose, flesh and blood. CAPTION: Picture, Photo of Elizabeth Drew by Stanley Tretick