The 11th floor at 666 Broadway looks like the home of some more rakish publication than the venerable Harper's Magazine.

After more than half a century in midtown, the 136-year-old monthly recently moved to this still slightly raw space in a district of surplus jeans stores and yet-to-be-gentrified manufacturing lofts.

Two cats named Jane and Paul (after writers and critics Jane and Paul Bowles) have taken up residence on the premises, using a litter box in an assistant editor's office.

Aside from father figure Lewis Lapham, the editorial staff is a youthful cadre in jeans and tweed jackets, assembled from The Nation, Commentary and the New York Review as well as the late SoHo News. They work hard and come cheap.

Boy Publisher John R. (Rick) MacArthur, 29, comes cheapest of all: He helped engineer the dying magazine's resuscitation by his family's foundation six years ago, took the helm as president and publisher three years ago, and still doesn't draw a salary.

This is the small-is-beautiful approach to the continuing problem of how to keep serious magazines afloat. Most thoughtful magazines with less than mass audiences survive through either deep-pocketed publishers or repeated fund-raising appeals to their loyal readers.

Both Harper's and its historic rival The Atlantic faced this dilemma a few years back. Each had about 325,000 circulation in 1980 and was losing serious money. In Harper's case, the losses amounted to a consistent $1.5 million a year, and the owners had announced plans to pull the plug.

The two magazines, however, responded in completely divergent ways. The Atlantic's new owner, Mortimer Zuckerman, has invested heavily in a long-range campaign to buy reporting and art, bolster circulation and sell ads. Industry sources estimate he's lost $10 million in the process, but The Atlantic has built its circulation to 450,000; it's gaining on The New Yorker.

Harper's, by contrast, hacked its circulation back to 140,000 (it has since climbed to 150,000). Its staff is now half the size it reached in its more celebrated days under editor Willie Morris in the early '70s. The product itself is a pared-down kind of publication, built for speed. It no longer really competes with The Atlantic, but it will lose "only" $150,000 this year, the Boy Publisher claims.

"I'm not in a position to subsidize Harper's," he cautions. MacArthur is a grandson of the late billionaire John D. MacArthur, who funded the foundation that gives those we're-not-supposed-to-call-them-"genius" grants. "I'm not poor, but I'm not rich enough . . . To some extent, I believe in the marketplace. If it survives, we're doing our job editorially. If not, better to let it go. The only way I want to be involved with [Harper's] is if it is self-sufficient, competitive, innovative; all those capitalist cliche's apply." And though it remains to be seen whether either the Harper's or the Atlantic approach can produce a healthy magazine, MacArthur says, "I'm not that worried anymore."

It had the elements of a kiddy crusade, all faith and crossed fingers, when MacArthur and Lapham launched Harper's most recent incarnation in 1983. There wasn't any business plan, and MacArthur admits that his business experience was limited to hearing his father talk at the dinner table. Lapham's concept -- weighty material packaged for people too busy to read weighty material -- sounded reasonable but wasn't subjected to any test marketing.

"It seemed it could work commercially, but it was all instinct," MacArthur acknowledges. "I went around saying I wanted the magazine to break even in three years -- and I'm on track -- but I pulled it out of the air. I didn't know if I could or couldn't."

For years, the news out of Harper's had been grim, generally involving insolvency or internal tumult or both. Its obit had run in 1980, when the Minneapolis Star and Tribune Co. had announced it was ceasing publication.

MacArthur had been among Harper's mourners. Then a Chicago Sun-Times reporter, he had helped persuade the MacArthur Foundation to buy Harper's and endow the $3.1 million Harper's Magazine Foundation. Still in critical condition, however, Harper's had marked its worst financial year in 1981. The red ink had reached $2.4 million, with the MacArthur Foundation covering the losses, and Lapham, editor since 1976, had resigned.

There had followed the brief and turbulent Michael Kinsley editorship, now rarely mentioned at Harper's. "We'd had this spectacular financial turnaround" -- losses had shrunk to $308,000 -- "and we'd won the National Magazine Award for general excellence and the day after we won it Rick MacArthur called me up and asked me to quit," is the way Kinsley, now editor of The New Republic, remembers it. (MacArthur responds that he was merely conveying what amounted to a board vote of no confidence, and that the circulation cuts Kinsley claims credit for had already been planned when he arrived.) There had been earlier flaps, the most publicized about an Israeli-sponsored tour of Lebanon Kinsley had taken; he eventually left in a swirl of mutual ill will.

From the wreckage, MacArthur and Lapham (whom MacArthur persuaded the board to rehire as editor) fashioned the new-format Harper's, unveiled to a skeptical public in March 1984.

The reviews for Harper's, from people who pay attention to such things, are still mixed. Being smaller, and not being the house organ for a particular political viewpoint, has cost it some journalistic clout; it is no longer a must-read.

But it survives, which MacArthur counts as a considerable achievement in itself. About $1.5 million remains in its endowment, thanks in part to a $500,000 gift from the late J. Roderick MacArthur, Rick's father, in 1984. The renewal rate is up; the rate base rises to 160,000 circulation in July. The esprit de corps in the new offices is almost tangible; the crusaders think they've pulled it off, pulled Harper's back from the abyss, again.

A reader's guide to Harper's: It features a spare design that, in Lapham's words, "doesn't make much concession towards splashy, Town and Country graphics" and in the words of Hendrik Hertzberg, a once and future magazine editor, "looks like a corporate annual report."

Leading off inside, there's Lapham's essay, "Notebook." Once characterized as a neoconservative, Lapham now seems to defy conventional labels. Other editors call him, variously, "part monarchist and part anarchist," "an oppositionist" and "a Tory."

Lapham himself says Harper's hews no political line, "in the sense of left-right," but is conservative "in that we try to preserve the tradition of written discourse, civility, the good elements in conservatism." This does not, he adds, put Harper's among the Reaganauts. "I don't think of them as conservative in the genuine sense; I think of them as trying to hold on to real estate."

Next comes the revamped Harper's single most noticed (and imitated) feature, a page of statistics called the Harper's Index, laboriously culled from dozens of phone calls and armloads of publications (reports to the chairman of the House Armed Services Committee, Radical America, Industrial Design). The Index can be pointed (minutes of ABC News coverage of South Africa in the month before last November's media ban, 10.8; minutes afterward, 3.2) or bizarre (the most popular television program in South Africa is "The Cosby Show") or peculiarly American (chances that a male North Dakotan is an Elk: 1 in 10).

Other Lapham innovations marking Harper's:

*The "Readings" section -- a pastiche of reprints that range (in the current issue) from an interview with Regis Debray to a three-paragraph Gordon Lish short story to a scientific study on dementia and Margaret Thatcher.

*An edited symposium called "Forum" (April's issue presents Jesse Jackson debating author Charles Murray on poverty, race and welfare.)

*And a document (a patent, a hospital bill, a funeral contract) with authorial comment, called "Annotations."

The remainder of the magazine's 80 pages are filled out with essays and criticism (often adapted from other sources), fiction on occasion, and a "Report," sometimes the only piece of original journalism in the magazine.

What most of these elements have in common is that they are inexpensively acquired; the most expensive component, original reporting, is the least used. "I'm sure [Lapham] had a lot of financial limitations and he had to design an interesting magazine within those," says Atlantic Editor William Whitworth.

Lapham defends his format as "more oriented toward how people think today. Look at a movie on late-night television that was made in the '50s and you can't believe how slow it is. We're used to thinking and responding at a different speed."

That it's a radical departure from the old Harper's is a point of pride. "People said what a swell, earnest magazine it was, but they never got around to reading it," Lapham says. "It piled up on their coffee tables like homework."

He gets no argument about the fact that it's a different publication now. "It's no longer Harper's and The Atlantic and 25 cents if you can tell which is which," says Hertzberg, the former speech writer and New Republic editor now involved in launching a political magazine. "It's no longer just Tweedledum to the Atlantic's Tweedledee. Lewis has made it unique."

Whether he's made it a first-rate magazine remains debated; it has champions and detractors, though people don't always fall into the category one might expect.

Among the champions, Victor Navasky, editor of The Nation: "I thought the new format would be a straitjacket, but . . . it permits all kinds of surprises. I look forward to receiving it."

Among the detractors, James Glassman, formerly executive vice president of U.S. News & World Report and president of The Atlantic, now a magazine consultant and author: "[Lapham's] idea that people want to read snatches of things is true if you're talking about mass audiences. But Harper's and The Atlantic and The New Republic and a few other magazines should be aimed at the minority who want to take the time to read something intelligent. I don't like the concept for that reason. I find it very unsatisfying."

Among the more neutral, Hertzberg: "It isn't really a vehicle anymore for really serious reporting and writing. In that sense, I guess you could say it's been diminished. But it's provocative and it's enjoyable."

Among those who say they rarely read Harper's: William Rusher, publisher of National Review, and Michael Kinsley.

"I really think we can do it next year," MacArthur is saying. Harper's doesn't require profits -- though it could reinvest any it happened to make. It does, however, want its income, including the interest on its endowment, to meet its expenses.

Next year, he muses, "I'd like to announce that the magazine is now in the black and, by the way, I'm going to pay myself a salary."

The current $150,000 deficit is "nothing," he maintains. "It's 40 advertising pages . . . I gotta get booze and cars -- that's where it's at."

"For that magazine, it'll be hard to get," predicts magazine consultant James Kobak, owner of Kirkus Reviews. Harper's does fairly well with corporate institutional advertising from the likes of Rockwell International and McDonnell Douglas, but remains weak in consumer product ads.

Wangling them from "booze and cars" means tackling "the two toughest nuts of all," according to magazine and newspaper consultant Richard LePere. He points out that the liquor industry is hard-pressed and that auto makers prefer to spend their ad budgets on television and newspapers. "The magazine industry is flat-to-down in terms of advertising pages and everyone's after the same dollars," LePere says. "It's going to be a mean trick."

Still, if Harper's really does lose "only" $150,000, it has enough in its bank accounts to keep publishing for years, and that cheers even the doubters.

It remains, after all, a monthly that reported on the Civil War, that published Stephen Crane and Sherwood Anderson as well as David Halberstam and Norman Mailer. MacArthur and Lapham might wince at the description of Harper's Magazine as part of American history -- they're trying hard to stop potential readers from thinking of it as an antique -- but the fact is that readers regard Harper's differently from Metropolitan Home or (Lapham's favorite example of the profitable and highly specialized magazine) The American Beagle.

"I hope it makes it," says Robert Manning, former editor of The Atlantic. "It'd be a shame to see Harper's go."