If the federal courts had a sense of humor, the case would be called Slime vs. Yuk.

Instead it is Mattel Inc. vs. Hot Items Inc., but Slime and Yuk are what the two toy companies are in court about.

Mattel, the nation's largest toy company and the inventor of Slime, has accused Hot Items, makers of Yuk, of copyright infringement and unfair competition for allegedly stealing its package design for the slithery product.

Mattel contends its multi million-a-year Slime business is slipping away because Yuk has copied its package design and undercut the price of one of the hottest toys since hoola hoops.

As almost anyone under 12 knows, Slime is the right-on accurate name for something "gooey, drippy, oozy, cold 'n clammy" that comes in garbage cans and has absolutely no function save to revolt adults and fascinate children.

Mattel sold $8 million worth of Slime last year and had orders for another $1.5 million in January.

Mattel spent $194,000 advertising Slime last year and will throw another $200,000 worth of Slime advertising at the nation's children by April, Mattel Marketing Director Richard A. Bailey said in an affidavit filed in U.S. District Court in New York.

Bailey said Slime sales started slipping in January after the virtually indistinguishable Yuk hit the market.

K mart, which bought $732,000 worth of Slime last year, tried to cancel an order for 90,000 cans in January, so it could switch to Yuk, which Hot Items allegedly offered at a 30 percent lower price than Slime.

Mattel contends it stands to lose unspecified millions unless the court orders Hot Items to end its alleged infringement of copyright.

Toy industry sources say the lawsuit focuses on the packaging because it is virtually impossible to patent or copyright a toy like Slime/Yuk.

So-called "knock-offs" of popular, but unpatentable products are common in the toy business as well as in clothing and furniture, where designs are difficult to protect.

Mattel's lawsuit says charging lower prices for copies "is typical of the toy business and is possible because the companies knocking off products of innovative companies like Mattel do not have developmental costs or advertising costs."

Mattel isn't saying what it cost to develop Slime and would not comment on the lawsuit.

Both Slime and Yuk are a "water soluble gel product," Mattel's lawsuit admits. Both come in regular and new improved versions which feature vinyl worms, sold as Slime Worms and Yukky Worms.

In stylized green letters on a purple background, the Slime can promises, "It's gooey, drippy, oozy, cold 'n clammy. For ages over 5." Yuk's green letters on a purple background assure buyers, "It's silly-chilly, ooey-gooey, glows in the dark. For ages over 5."

Mattel complains that the back of the Yuk can is "a virtually verbatim copy of the back portion of the label of the Mattel product."

The makers of Yuk, located in Newark, N.J., could not be reached for comment yesterday.

Mattel, headquartered in Hawthorns, Calif., reported sales of toys and models of $316 million last year, plus another $69 million in revenues from related businesses, including Ringling Brothers Barnum & Bailey Combined Shows. The Ringling subsidiary has executive offices in Washington.