The X-Men Want the Night Too : Merchandising: The Marvel comic characters have conquered Saturday morning TV. Now they are heading for a bedroom near you.

X-Men, on a trajectory to superstardom for 30 years, have finally arrived.

They began as Marvel comic book characters and went ballistic two seasons ago on Saturday morning television. Then the marketing machine began to churn. Action figures, clothing, lunch boxes and video games have spewed forth with amazing speed.

Now, the pinnacle of merchandising excess has been reached: X-Men are being emblazoned on bed sheets that will be in stores for the holidays.

If you don’t know these monster mutants, you soon will:

* The “X-Men” show on the Fox Network is the No. 1 cartoon with kids 6 to 17. It attracts both boys and girls--and almost half the audience is over 18. It seems the characters--more than 200 and counting--who attack the forces of intolerance are politically correct by ‘90s standards.

“It has every thing that a child or an adult could want in an action-adventure fantasy,” says Margaret Loesch, president of Fox Children’s Network. “Its got pathos, its got mystery, its got colorful characters, good and bad characters. And the interpersonal dynamics are very interesting,” she says, trying not to gloat.

* The X-Men comic books have been at the top of the industry charts for 12 years, says Bob Harras, X-Men’s editor at Marvel Comics. There are more than 10 spinoffs of the original X-men, including Junior X-Men, X-Force and X-Calibur, the British arm of the X-Men.

* The X-Men had their own fast-food tie-in last summer, Pizza Hut’s eight-week meal deal.

* The five-inch-tall X-Men action figures, $5.99 to $6.99, have toy store cash registers ringing like Vegas slot machines. More than 14 million of the plastic hunks and hunkettes have been sold in the last two years. And new figures arrive every month. Kids want every one. Toy store managers say they are besieged with calls from parents and children looking for the latest, hottest character. Even Loesch has fielded calls from kids on the availability of X-Men.

* The X-Men trading cards have been banned by one Massachusetts after-school program because of their disruptive influence.

* And earlier this month Avi Arad, president of Marvel Film, met with the owners of the big desk sets at 20th Century Fox to sign agreements for a live-action X-Men movie.

Those who want to get with the X-Men craze can either hang around a playground and get the X-Men lowdown from an 8-year-old or read the following:

X-Men: Mutant teens of both sexes who attend a magnet school for gifted students. Each has become physically enhanced in a different way by the effects of radiation poisoning. Sabretooth, for example, has sprouted a frightening display of teeth in desperate need of orthodontia and a permanent set of Lee press-ons.

Their Mentor: Professor Xavier, aka Professor X, who can communicate telepathically with his charges. He believes humans and mutants will one day live together harmoniously.

Their Nemesis: Magneto, who has a skinhead mentality.

Big X-Men on Campus: Wolverine, a loner and reluctant team member with a Type A personality who has retractable claws and can instantaneously heal his own wounds.

Cyclops, the mutant teen leader, who is extremely focused and emits a powerful optic beam that can be controlled with fashion accessories such as visors and sunglasses.

Storm, the second in command, who can fly and control the weather with a flick of her wrists but is hampered by claustrophobia.

The Look: Super heroes come in super-steroid or super-silicone shapes. Their costumes are possible thanks to the invention of spandex. They never have bad hair days.

Catch Phrases That May Make Their Way Onto T-shirts: Wolverine calls everyone “Bub,” say the powers at Marvel. They expect the innocuous “Bub” to become a T-shirt-worthy X-Menism.

Insignia: An X-Men school crest--a shield with the words Professor Xavier’s School for Gifted Youngsters-- is finding its way onto clothing. A red X in a black circle is the X-Men symbol.

The Attraction: “They’re all kids and they’re fun cause they’re mutants,” says Eric Korpie, 9, of Reseda. He is a big fan of the TV show, has 15 action figures and vows to collect them all. He and his neighborhood friends often play a game they call “us,” in which each adopts an X-Men persona. They zoom about the streets battling imaginary Magnetos and the evils of prejudice.