Steve Milo will arrive at work today secure in what is perhaps the best knowledge an entrepreneur can have: He is going to do a spectacular amount of business this week.

Milo, 27, is the founder and president of American Entertainment Inc., a mail order company based in Gainesville, Va., that delivers a fun product -- comic books -- and racks up some serious sales. On its best days, the company, which has a mailing list of more than 100,000 people, can pull in up to $50,000, Milo said.

But all that may be just a warm-up for Friday, which promises to be one of the biggest days in the history of comic books, and thus, in the history of Steve Milo.

That's the day Marvel Comics will release X-Men No. 1, a new title featuring its most popular characters. The press run is estimated at 7.5 million copies, well above previous industry records of 3.6 million for X-Force No. 1 in June and 2.7 million for Spiderman No. 1 in July 1990.

The X-Men are a collection of persecuted mutants dedicated to the fight for the good of humanity. A mutant, by the way, is born with supernatural powers. That's different from a super hero, who must acquire such powers. For instance, comic book character Peter Parker became a super hero named Spiderman after he was bitten by a radioactive spider.

Marvel Comics is the country's top comic book company. Its characters include the X-Men group, Spiderman and Captain America. Internal Correspondence, a trade magazine, estimates that Marvel will likely capture more than a 68 percent share of the comic book market this month because of sales of X-Men No. 1. Most of the rest of the $350 million annual comic book market belongs to DC Comics, creator of such characters as Batman, Superman and Wonder Woman.

Milo, who started his business from a dorm room at the University of Virginia when he was 20, gets his piece of the comic book pie in three ways. He has a Georgetown retail store called Another World and he has his mail-order business, which is split into two operations. One sells upcoming issues at a discount and the other sells back issues at a premium. His Gainesville warehouse is stocked with more than 1 million comics. Thirty employees spend each day logging, filling and shipping orders nationwide.

There are only about a half-dozen companies nationally that do the bulk of their comic book sales by mail, according to Milo and Terry Stewart, the president of Marvel Comics.

Stewart said he met Milo at a trade event and came away impressed.

"He has some unique marketing visions," Stewart said. "I think {mail-order retailers} supply a very needed service. There are folks who because of their lifestyle, or because of distance, can't get to shops."

Stewart said Marvel has its own subscription service but said it is "not anything that's going to make anybody very happy. It takes too long."

Milo has ordered more than 200,000 copies of X-Men No. 1. The book will be published in four regular editions, each with the same content but a different cover, and will retail for $1.50 each. The book also will be published in a special $3.95 edition featuring a fold-out of the first four covers plus a fifth cover. Milo, who declined to reveal how much he pays for a comic book before reselling, said many of his customers want every edition.

"X-Men No. 1 is not just a comic, it's an event," said Milo, sitting in an office packed with crates of orders for the book. "X-Men No. 1 appeals to virtually every Marvel reader."

More than 100,000 people receive American Entertainment's colorful monthly catalogues, which Milo writes and helps design. He said the average customer spends $50 a month on comic books. Ninety percent are male and their median age is 18.

Through X-Men No. 1 book sales and sales of related products such as calendars, T-shirts and trading cards, Milo expects revenue of more than $500,000 this month. Last year, he did nearly as well with the release of Spiderman No. 1 and American Entertainment had annual sales of about $3 million. This year, largely because of the back-to-back releases of X-Force No. 1 and X-Men No. 1, the private company expects $5 million in sales.

"This is the biggest heyday for comics since the 1930s," said Thomas Stormonth, director of purchasing at Baltimore-based Diamond Distribution, the world's largest comic book distribution company.

Stormonth said retailers such as Milo are especially well-poised to take advantage of the boom as long as they are astute in placing orders. Knowing how many extras to order can mean big money for a retailer once the comic book is out of print because the price will rise quickly in many cases. As the book gets older and becomes more difficult to obtain, the price will continue to rise.

"I knew stores that sold out of X-Force in the first two days, not because they sold thousands and thousands but because they sold out of their 150 copies and then they couldn't get any more," said Joseph Gumbinger, owner of Burke Centre Used Books and Comics in Burke and Franklin Farm Used Books and Comics in Chantilly.

Gumbinger said he ordered 5,000 copies of X-Men No. 1 for his Burke store and 1,500 for the Chantilly store.

"Steve Milo's probably ordering 500 cases," Gumbinger said. "But for us, 5,000 of one comic book, it's staggering."