At fifty-one, Robert Wilson, bearded intellectual, devotee of the arts and world traveler, is at the peak of his career. He's the stock market's Batman, Superman and Six-Million-Dollar Man all rolled up into one. But the man who has dazzled Wall Street with his extraordinary market skills - his assets have shot up roughly thirtyfold, or grown at a compound annual rate of nearly thirty-five percent between 1965 and 1977 - has reached the stage, he tells me, where his battery needs recharging. Such popular battery refreshers as a more active (and diversified) sex life, tennis and weekly visits to the local health club leave him cold.

And so Wilson, largely unknown to theinvesting public because most of his dealings are for his own account (he also manages a small hedge fund), is planning to leave the currently erratic and tension-filled investment scene for a lengthy sabbatical. Beginning May 1, he will embark on a six month pleasure trip throughout Europe and the Far East, and during that time he will not make any new investments. His only traveling companions will be the silent type - Keats, Shelley, Wordsworth, James Joyce and the complete works of Shakespeare.

If he's right, Wilson's vacation could have dismal - and significant - overtones for investors. The message: maybe the ought to take a vacation, too, since the latest man to be described as "The Wizard of Wall Street" is strongly convinced that the ailing stock market - which recently struck a three-year low and is suffering badly from a sliding dollar and Jimmy Carter's inept performance as President - will continue in the doldrums for quite a while.

"I'm not going away in a fit of pique or depression, but to revivify myself," Wilson told me at dinner the other week (after grumbling about his salty quail). Added the always confident, self-assured Wilson: "I've always considered myself a moneymaking machine in any kind of market. But if you want to keep a machine well maintained, you simply don't operate it at full capacity: you take time out for repairs. And the older a machine gets - like me - the more time it requires for repairs." Then breaking out in an elfish grin as he frequently does, Wilson quipped: "I'm really following Cicero's dictum: If one should live it slowly. And I've never taken six months off . . . except for nine months is the womb."

Wilson, who was up a hefty 25 percent in last year's sharply declining market, and who is up another four percent in 1978, says he probably would not make the trip if this were a more exciting market period.

But he's not expecting very much over the next six months. "This is a very stagnant time," he observes. At most, he sees the market drifting down another 10 percent or so, or perhaps rising five percent. "Everybody is bearish," he says, "but that's already discounted in the market's sharp decline in the last 13 months . . . so I'm not looking for any disaster this year."

Wilson thinks the market's abominable showing is chiefly a reflection of "the utterly dismal economic outlook." For starters, he points to rising interest rates, accelerated inflation, declining corporate profits and the dollar's continuing under siege. But more significantly, he views the whole U.S. economy as decadent, declaring: "It's suffering from English sickness." He defines this sickness as a reflection of inadequate capital investments, lack of incentives to prompt people to work hard and artificially inflated prouduction costs due to government harassment and regulations.

Accordingly, he sees stock prices - save for periodic rallies - sliding another 30 percent or so over the next several years.

With such a grim outlook, one might expect Wilson's portfolio to be heavily weighted in favor of his great specialty - short sales. Not so. His long position (the stocks he own) always exceeds his short position (the stocks he's betting will go down) because, as he explains it, "I never want to be in a posture where I hope things get worse. And there are always stocks that run counter to the market."

His current favorites are the real-estate investment trusts, notably the equity trusts (those that own their own properties, rather than lend money on them). The chief reasons he like them: a rising real-estate market, the big discounts (in stock prices) from book value, and sharply rising construction costs (which tend to discourage new building). All told, Wilson owns 27 different trusts.

Wilson also likes the computer stocks because he views the industry as one of the few American businesses that's still creative and ahead of the rest of the world. His top choices: Cray Research, Commodore International and Data Point. Other favored securities: Tandy, Addressograph-Multigraph, Advent, Avco, Teledyne and Technicon.

It's always interesting, of course, to know what a market whiz is buying. But in Wilson's case, it's probably more interesting to know what he's selling short because he's regarded by some sophisticated Wall Streeters as the best short seller in the business.

Which stocks are the best shorts in the market? Wilson puts the containerized shippers (Flexi-Van, Interway and Sea Containers) at the top of the list. In the past 18 months, the rates and utilization of sea-container companies have risen dramatically, but Wilson expects a marked slowing of growth on both counts.

Other favorite Wilson shorts include Dow Chemical, International Paper, British Petroleum, Tom Brown, Colonial Commercial Air Products, National Presto (which fell sharply yesterday because of poor earnings), Applied Digital Data, Centronics, Advanced Micro Devices, International Systems & Controls, Resorts International and Technicare.

With Wilson frequently dabbling in volatile and at times questionable stocks, his market activities, not surprisingly, have caught the eyes of the Securities and Exchange Commission. In fact, Wilson, at this very time, is one of several leading short sellers being looked at by the S.E.C. in connection with a lawsuit filed by a Manhattan dentist. In that suit the dentist, a Technicare shareholder, alleged among other things, that Barron's columnist Alan Abelson was tipping off a group of short sellers, including Wilson, to upcoming Barron's stories. And that allegation - which I regard as absurd - is something the SEC has been talking to Wilson about in recent meetings. (Abelson has written negatively about Technicare on a number of occasions.)

Wilson, who has never been named in an S.E.C. action, is boiling at the commission. "I'm not as anti S.E.C. as others on Wall Street, but they're trying to intimidate me, to inhibit free speech, and I'm not going to let them do it," howled. Wilson, a friend of Abelson's for about ten years, went on to say, "If I have a thousand ideas for Alan, I'll call him up with all of them. I'll shoot my mouth off as I see fit, talk to anyone I want . . . to whores or any one else. And I've made that clear to the S.E.C."

Wilson, who'll be away for six months in a clearly treacherous market environment, could, of course, simply liquidate his entire portfolio and put the money into some safe money-market instruments (such as Treasury bills or bonds). That way he needn't worry what happens when he's away. That's not Wilson's game plan, though. "I'm going away fully invested but rather well hedged (a reference to his short position), to protect myself against any major market decline," he says. "Besides, I love playing the market and I'm comfortable with my positions."

In the event one of his positions should be liquidated, Wilson will put into effect a plan whereby any of his brokers can send him a Telex and explain why the investment should be terminated. He will accept no phone calls, which, he says, "I find jarring and upsetting when I travel." Adds Wilson: "I've hardly had an original thought in my life. I'm not a self-starter, but a reacter with vigor. Virtually every stock I'm in, some broker has put me into it. And I expect my brokers - whom I love because they're the reason for my success - to watch over my positions when I'm away."

Wilson has only one reservation about his upcoming trip. And it's worth noting because it is one of the chief reason for his successs.

"Everyone thinks the trip's a great idea," he says," and that worries me. When everybody thinks alike, you know they're wrong. If there is one thing I hate, it's big majorities in anything."