Roy Collette and his brother-in-law have been exchanging the same pair of pants as a Christmas present for 11 years - and each time the package gets harder to open. This year the pants came wrapped in a car mashed into a 3-foot cube. The trousers are in the glove compartment of a 1974 Gremlin. Now Collette's plotting his revenge--if he can get them out.

It all started when Collette received a pair of moleskin trousers from his brother-in-law, Larry Kunkel of Bensenville, Ill. Kunkel's mother had given her son the britches when he was a college student. He wore them a few times, but they froze stiff in cold weather and he didn't like them. So he gave them to Collette. Collette, who called the moleskins "miserable", wore them three times, then wrapped them up and gave them back to Kunkel for Christmas the next year.

The friendly exchange continued routinely until Collette twisted the pants tightly, stuffed them into a 3-foot-long, 1-inch wide tube and gave them back to Kunkel. The next Christmas, Kunkel compressed the pants into a 7-inch square, wrapped them with wire and gave the "bale" to Collette. Not to be outdone, the next year Collette put the pants into a 2-foot-square crate filled with stones, nailed it shut, banded it with steel and gave the trusty trousers back to Kunkel. The brothers agreed to end the caper if the trousers were damaged. But they were as careful as they were clever.

Kunkel had the pants mounted inside an insulated window that had a 20-year guarantee and shipped them off to Collette. Collette broke the glass, recovered the trousers, stuffed them into a 5-inch coffee can and soldered it shut. The can was put in a 5-gallon container filled with concrete and reinforcing rods and given to Kunkel the following Christmas. Two years ago, Kunkel installed the pants in a 225-pound homemade steel ashtray made from 8-inch steel casings and etched Collette's name on the side. Collette had trouble retrieving the treasured trousers, but succeeded without burning them with a cutting torch.

Last Christmas, Collette found a 600-pound safe and hauled it to Viracon Inc. in Owatonna, where the shipping department decorated it with red and green stripes, put the pants inside and welded the safe shut. The safe was then shipped to Kunkel, who is the plant manager for Viracon's outlet in Bensenville.

Last week, the pants were trucked to Owatonna, 55 miles south of Minneapolis, in a drab green, 3-foot cube that once was a car with 95,000 miles on it. A note attached to the 2,000-pound scrunched car advised Collette that the pants were inside the glove compartment. "This will take some planning," Collette said. "I will definitely get them out. I'm confident." But he's waiting until January to think about how to recover the bothersome britches. "Wait until next year," he warned. "I'm on the offensive again."