A pro: That which fosters fairness for the most stockholders is best

He makes millions on these deals - but he's just as likely to lose millions. Such are the fortunes of an arbitrager. Ivan F. Boesky is one of the most successful ''arbs'' in the business. He is not a takeover artist, though. More like a speculator.

Mr. Boesky maintains an extensive network of intelligence gatherers to find out about possible acquisitions early on. Then he buys stock in a company that is facing acquisition, aiming to sell at a handsome profit if that company is acquired by another.

He made millions on the Gulf sale to Chevron, but Boesky does not always win big. The two-tiered offer that Disney made to financier Saul Steinberg last summer allowed Mr. Steinberg to sell his stake for $77 a share. But other investors, including Boesky, had to sell at $48. That hurt.

Such ''greenmail,'' Boesky said in a recent telephone interview, is an abuse: ''We have suffered from such abuse. We never engage in that activity.'' Boesky's philosophy (delivered, with numerous interruptions, from his busy New York office): ''That which promotes fairness to the most stockholders is the best.''

Many corporations are vulnerable to raiders, he says, because they get the wrong advice: ''They're told that they'll be protected if they wear armor. Instead they should be told how to avoid the battle. And you do that by being mindful of your securities and management and the operation of your company in a fashion that causes securities to be fairly valued.''

Boesky says the prime directive for corporate managers is that ''they are running a company for the owners - the stockholders.'' These owners buy stock not out of a warm feeling for the company but because they want the stock to go up. If the stockholder has to wait forever for this to happen, ''he may be a disgruntled owner,'' Boesky says.

To help a corporation prevent this, Mr. Boesky's other hat is that of ''merchant banker'' - a role he defines as taking a ''friendly'' position in a corporation to teach it ''how to run a company in the owners' interest.'' Any other way, he says, simply ''makes lawyers and accountants rich.''