Nothing less than the whole vast panoply of human existence is represented in magazines debuting this month. Nonbelievers, read on:

The good - Washington Baltimore Singles Magazine and Date Book, which primly describes itself as "a clean, non-sex magazine offering an above-board decent way to meet." Interested parties simply purchase ads - minimum cost is $7 - and wait for those cards and letters to discreetly pour in.

An offshoot of successful Date Books in New England and Philadelphia with a corporate motto of "there are no strangers here . . . only friends who haven't met." the Washington version is published by Gene Valentino, who says, "We take nothing obscene. No 'Well-built 29-year-old gay looking for S-M treatment." none of that goes in. If someone sends in something questionable I write or phone them and say, 'Hey clean up your act, I'm very sensual too, but there's a subtle way.'"

The led - Assassin, ripping the lid off "The Secret World of the Killer Elite." has according to publisher David Kornblum, "gotten off no pun intended to a bit of a hang."

Kornblum, who squads properly conspiratorial over the phone says he spent three years "putting together an advisors panel of realty high-grade international mercenaries. This is not a book about gardening, information is hard to come by. But I seem to have known the wrong kind of people for as long as I can remember."

By publishing stories like "Sex and the KGB," and "Be The First on Your Block to Build a Nuclear Weapow." Kornblum claims to be counteracting the appalling glamor put out about people like James Bond. These people are not the kind of people who are well-adjusted". And he adds quietly just before hanging up. "If we can ever do you a favor, just pick up the phone."

The ugly - Only for the strong of stomach is Violent World, with premier issues featuring graphically illustrated articles like "The Baby Masscare" and "Killer Sharks Invade Shallow Water." Shades of the old National Enquirer, except says editor Jesse Leaf. "I think we're better graphically. And our stuff is all true, nothing is staged."

A former editor at Genesis as well as an ex-CIA employee. Leaf says his magazine exists because "there's so much violence, tragedy and horror going on in the world, we thought it would be a good idea to put it all together."

And not that there isn't room for a little levity in all this Watch for a piece on the Notorious Downtown Toe Stomper, "a guy running around Atlanta stomping on people's toes". As for Leaf's own tastes, he says he's "personally opposed to violence. I'm a pussycat." Mr. Fun

Better let Stanley Marsh 3 (nee III) describe himself. No one else could do him justice. "I fullfill whims," he says. "Most people have whims and dreams, and I'm just lucky enough to carry out my whims . . . If there were more people like me, it would be a more interesting world."

Marsh a wealthy Texan who is the self preclaimed U.S. Professional Fun Champion, has whims like nobody's business. As catalogued in the April 13 Sports Illustrated, they include the following:

writing Pat Nixon saying he was thinking about opening a Museum of Decadent Art and wanted samples of her wardrobe to fill up the entire first floor.

dyeing a Clydesdale blond and painting its hooves pink.

giving a home to the Cadillacranch, ten Cadillacs half-buried engine down in concrete sheaths at the exact angle of the Great Pyramid. "Once you've seen that," says Marsh, "your reality is changed forever. Never again can you be so sure that you know what you're going to see."

writing the word TRUCK in big neat white letters on his truck "so you can tell it apart from a carrot."

putting up a sign near a planned housing development reading "Future Home of the World's Largest Poisonous Snake Farm."

Not that Marsh gets around to everything he'd like to do. One as yet unfinished plan is to "cut out a huge hand shape on my ranch somewhere - 500 acres or something - plant wheat in it and call it The Great American Farmland." Complains the Fun Champion. "I haven't got the time to be as crazy as I'd like." The Big Ten

The newly released A.B.C. magazine circulation figures reveal only one change in the top ten magazines in the six months since the last count. Woman's Day moved up to the No. 4 spot, gaining 400,000 readers and bumping Family Circle, despite a gain of 100,000 to No. 5.

People remained a phenomenon, moving from No. 28 to No. 21 and gaining nearly 300,000 to push its circulation just over 2 million. But the biggest success story was Hustler, which gained half a million readers to go to 1.9 million and moved from No. 37 all the way to No. 23. A year ago Hustler had only 826,000 circulation and was No. 62. In a perhaps unrelated development, both Boys Life and Scouting dropped in the list.

The top ten include:

1 - TV Guide 20,226,757

2 - Reader's Digest 17,887,299

3 - National Geographic 9,350,123

4 - Woman's Day 8,582,538

5 - Family Circle 8,576,213

6 - Better Homes & Gardens 8,094,553

7 - McCall's 6,524,126

8 - Ladies' Home Journal 6,088,117

9 - Playboy 5,541,004

10 - Good Housekeeping 5,412,727

P.S. Better Homes & Gardens reports that its May number was the biggest advertising revenue-producing issue of any magazine ever. Total take was $8,254,237, nosing out the October, 1976 Reader's Digest, the former champ. Busy, Busy, Busy

Anytime you think you're working too hard, think about Paul Erdos, one of the greatest living mathematicians, publisher of more joint papers than anyone in the world, a man so devoted to his work that, says the April 8 Science, nothing else exists for him.

Taking advantage of the fact that mathematicians need nothing but pencils and papers to do their work, Erdos has "eliminated all the normal encumbrances of daily life. He has no properly ('Property is a nuisance') and no fixed address; he neither handles his money nor fills out his income tax ferms." Constantly traveling around the world and staying with other math folks and their families, he will often walk into a room and immediately begin to discuss mathematics "without even explaining his presence or exchanging greetings first."

To top it all off, Erdos, described as a short, active man who "jumps up and flaps his arms when he has an amusing thought." sleeps only four hours a night, writing in mathematical diaries while lesser souls rest. When his friends tell him he is pushing himself too hard, he replies. "There is plenty of time to rest in the grave." Identify Crisis

Can a magazine turn itself into a book? Can a book also be a magazine? The answer is yes, twice.

The magazine that became a book is the venerable Atlantic, which has just published a 623-page tome entitled "119 Years of the Atlantic" and featuring one article from each of those years. But why 119 years?

"It was one of those sort of off-beat notions," says Atlantic editor Robert Manning. "We thought we'd skip the round number fixation."

The collection originated as a way to attract new subscribers and has in fact gotten some 30,000 into the fold, which naturally pleases Manning. What doesn't please him is that readers confuse his magazine with you know what.

"Yes, it still happens," he says. "People say to me. 'That was an interesting piece you had,' and it turns out to have been in Harper's. It's irritating, but we're not as much alike as we used to be."

The book that is really a magazine is Pages, an elegant, delightfully thoughtful once-a-year hardcover publication that is, according to editorial director Matthew Bruccoli, "a non-scholarly journal that deals with authorship, literary history and the book world, the book from womb to tomb."

Pages, which Bruccoli says is "either a magabook or a bookazine," came about because "as a professor of English of 20 years standing it drives me nuts that after four years of college most English majors just drop out of the subject. If I was a doctor, I'd have to admit most of my patients died on the operating table."

A literary life support system. Pages costs $24 per year and can be ordered from Gate Research Company, Book Tower, Detroit, Mich. 48226. Us Versus Them

The first two times People raised its price, it put Paul Newman on the cover. Could it be more than mere coincidence, then, that Us, the New York Times-backed personality magazine, put Newman on the cover of its premier May 3 issue?

"I think it's fair to say," says Porter Bibb, the Times Corporation's Director of Magazine Development and Acquisitions, with a smile, "that we have analyzed People's circulation figures with microscopic intensity."

Bibb is smiling because he is constantly being "backed up against a wall and pistol-whipped for ripping off People." He doesn't really mind, though, because "the philosophy we're using is that Life and Look left 15 million magazine buyers without any form of news-in-pictures. People took two million. That still leaves 13 million."

Outside of his Times work, Bibb has helped launch magazines as diverse as Working Woman and Andy Warhol's Interview, and, he is pleased to announce, he is currently working with something called CB Bible. Issue one features the gripping "I talked to God on my CB radio," while issue two will headline "'I Give My Baby CB Fever' By a Young Mother."

Over and out. The Boys in the Boat

When Errol Flynn showed all that interest in Olivia de Haviland in "Captian Blood," he was probably just being polite. For according to a piece in the current American Heritage, the Carribean pirates of the 17th and 18th centuries were homosexuals.

This startling bit of data comes from one B. R. Burg, associate professor of history at Arizona State, who did a "situation analysis" of the situation and reached his conclusion despite an admitted lack of detailed accounts of pirates' sexual lives.

Yet Burg maintains> "fo'c'scle humor abounds with tales of below-deck encounters where salty bo's'uns initiate tender cabin boys into the arcana of the seas, and even among the driest landlubber there are few who ever assumed that tedious months aboard ship were whiled away only by carving scrimshaw and singing chanties."

So much for 'Yo ho ho and a bottle of rum.' Mr. Big

United Press International

After dazzling performances in films like "Mean Streets," "Godfather II," and "Taxi Driver," Robert De Niro has emerged as perhaps the hottest young actor in America. But does that mean he's easy to talk to? Not on your life. In fact, claims Marie Brenner in the sob-sisterish. "What's Robert De Niro Hiding" in the May Redbook, he goes, so far as to keep his friends "under strict instructions to defend the wall of secrecy he's built around his life."

So what's he really like? Says an old girl friend. "Once you penetrate all the paranola and secrecy that Bobby surrounds himself with, you'll find out that at the bottom Bobby is really . . . nothing ." Says actress Shelly Winters. "In between pictures, Bobby doesn't exist. I don't know where the human being is." Adds Paul Schrader, the "Taxi Driver" screenwriter. "He doesn't feel the need to establish an identity apart from his screen personal. He doesn't want to. The only thing he wants public about himself is his work. Thats the only thing he believes has any real value.

So be it. Tidbits

Those who start ruzors are rumoring that Rolling Stone is considering going to slikc paper and a Time-sized format. "Definitely not," says a Stone spokesperson, conceding there might be a mockup around but adding. "They're always making mockups. They looked into staples for 10 years before it happened." More concrete is Outside, Stone's new outdoors magazine billed as a combination of National Geographic, Scientific American, Sunset and the Whole Earth Catalog. The preview issue will be out in May and regular publication will start in the fall . . . Both New York and More report that Fortune is close to moving to a twice-monthly format . . . You may be tired of Farrah Fawcett Majors, but some people aren't. Charlie's favorite Angel appeared on three major covers last month, including McCall's, Woman's Day and even Vogue, with a six-page fashion spread by Richard Avedon inside. The lady is even elbowing into Cher's gossip turf: the cover of TV Star Parade claims "Farrah 'Leaves Home' To Go With Sonny! 'Jealous' Cher Walks out!"

Almost as popular is Rudolf Nureyev, whose upcoming film debut as Valentino has gotten him an article in Ladies' Home Journal, a cover in Saturday Review, and "Exclusive Photos by Lord Snowdon" in Gentlemen's Quarterly . . . Sport Magazine has come a long way, baby. It's May cover, featuring femine golfer Jan Stephenson, is terribly saucy, and inside s a trio of articles on "Sex In Sports - A Key To Winning." . . . Princess Caroline of Monaco, if McCalls is to be believed, reads the novels of Colette and Emile Zola before retiring and prefers Mahler and leave in maninoff to rock . . . The 1977 National Magazine awards went to Architectural Record, Audubon, Harper's Mother Junes, Philadelphia and Rolling Stone . . . Jimmy Carter was apparently so tickled by Eisquire's March cover, which showed him minus a few teeth, that he signed up for a year's worth, the first paid White House subscription in Esquire history . . . Sign of the times is a cover line on the latest edition of 4-Wheel and Off Road magazine by the editors of Hot Rod "Bullerproof Your Off-Road Vehicle."