SEATTLE — Dean Peterson is a man on a mission. With a kilt.

Peterson, 48, a 6-foot-tall, 250-pound mail carrier in Lacey, wants the U.S. Postal Service to add kilts as a uniform option for men.

The idea was soundly defeated in July at a convention of his union, the 220,000-member National Letter Carriers’ Association, so Peterson knows convincing management will be an uphill struggle, but at least he’ll be comfortable in his kilt, or “male unbifurcated garment.”

“In one word, it’s comfort,” he said. With his build, Peterson said, his thighs fill slacks to capacity, causing chaffing and scarring.

A 22-year Air Force veteran, avid gardener and father of two teenage boys, Peterson has never considered himself an activist. He has Finnish and Norwegian ancestry but not Scottish.

He began wearing kilts a couple years ago when his wife brought one back from a trip to Scotland. Now he wears them everywhere — to a son’s football games, the other son’s concerts, shopping and gardening.

“Its the difference between wearing jammies to bed and wearing your work clothes to bed,” Peterson said.

While his prototype is the same color as other uniform items, an official USPS tartan is registered with the International Tartan Index.

A spokeswoman for Britain’s Royal Mail said kilts are not allowed as part of its letter carrier uniforms.

Before the convention in Boston, Peterson spent his family’s $1,800 economic stimulus tax rebate to mail about 1,000 letters and photographs of him wearing a prototype Postal Service kilt to union branches in every state, Guam and Puerto Rico.

“Unbifurcated garments are far more comfortable and suitable to male anatomy than trousers or shorts because they don’t confine the legs or cramp the male genitals the way that trousers or shorts do,” he wrote. “Please open your hearts — and inseams — for an option in mail carrier comfort!”

The union’s executive committee recommended disapproval, saying there was not enough demand for kilts to be worth the bother of the resolution, and delegates agreed by a large margin.

It was not a major issue at the convention, union spokesman Drew Von Bergen said.

“We were there doing a lot of serious things at the convention about the postal service, the economy, the union,” he said.

Union President William Young said he wouldn’t wear a kilt.

“That got my blood going,” Peterson said. “Even if there are only 300 carriers that want the option of wearing a kilt, we should have that option, and that’s why I’m fighting for this resolution.”

There are plenty of approved uniform items that very few mail carriers wear, including a cardigan sweater, vest and pith helmet, he said.

For an article of clothing to be approved as a uniform option, the union must first agree, followed by testing by a Postal Service Committee and selection of a manufacturer.

Earlier this year letter carrier unions in Washington and Oregon passed identical resolutions endorsing kilts.

Kilt enthusiast Paul Lunde led the effort in Oregon.

“As someone who walks 10 miles a day, when it gets hot, muggy — it gets hot, sweaty, chaffy,” Lunde said. “With a kilt, it doesn’t get as hot. There’s less chaffing.”

Unlike Peterson, Lunde has been allowed to wear a kilt to work on St. Patrick’s Day, Halloween and National Tartan Day on April 6.

He has heard negative comments from only three of his 100 co-workers and none from customers on his route.

Superiors and union leaders, however, have “already made up their minds. Unfortunately, their mouths are far more open then their minds,” Lunde said.

He thinks kilts look professional and would encourage esprit de corps.

“Whenever you see someone in a kilt, they’re always standing tall,” Lunde said.

Peterson said many convention delegates did express support after his resolution was voted down.

“I got so pumped up after being at such a low that I’m taking this to the next convention in 2010 in Anaheim, California,” he said.