Never mind that Cliff Long has a master's degree in history or that he speaks an authentic 17th-century English accent that would make a Hollywood coach proud.

These days, visitors to Historic St. Mary's City, where Long is an interpreter of living history exhibits, usually have just one question when they see him wearing layers of heavy linen and wool in the 90-degree heat: "Aren't you hot in those?"

"No, not at all. This is simply proper wear," Long told one tourist in yesterday afternoon's hazy heat in St. Mary's County. He was wearing ankle-length boots over stockings, heavy linen sailor pants called slops, a white linen shirt and a lined wool doublet, a buttoned vest--all the accouterments of a 17th-century shipmaster.

In truth, Long and the two dozen other costumed interpreters of Colonial American history at Historic St. Mary's City--Maryland's first capital just up the Potomac from the Chesapeake Bay--are sweating buckets of authenticity as they make-believe Colonial life for visitors in tank tops and shorts.

"Aye, it's summer. It's hot," said Lynn Ryan, who portrays Mistress Spray, the woman of a 1641 plantation house next to the St. Mary's River.

"It's just the way it is," said Ryan, slipping out of character, but remaining in her heavy linen bonnet, and over that a straw hat. She wears the women's fashion of Spray's day: a calf-length shift laced at her throat, a boned and lined bodice over the shift, a floor-length raw linen skirt, knee-length stockings and leather shoes that look like modern-day Mary Janes.

Standing at the doorway of the plantation house yesterday, overlooking the garden she had weeded in the morning, she said she was cool enough. But she did not look cool in all those layers of clothes.

There are some concessions when temperatures rise to 90 degrees or higher. Ryan and other women of Historic St. Mary's City wear one skirt instead of the usual two, and they can do without the "hip rolls," the hip pads that were the fad of 1641.

"I do without a bra," said Heather Loeffler, 23, who is a recent graduate of St. Mary's College of Maryland and a costumed interpreter at the plantation house. She is outfitted similarly to Ryan--braless is authentic--but she has shed her blue stockings and shoes. This too, is allowed.

"It's OSHA," said Karin Stanford, spokeswoman for the outdoor museum, referring to the federal agency that administers regulations on employee safety. As much as being authentic counts in portrayal of life in an English settlement, "you also use common sense," when it comes to safety in dangerously hot weather, Stanford said.

That applies to the tin bucket behind a shed and out of sight to visitors. It's filled with cool water.

"You soak your legs in there up to your knees, and it cools you off right away," Ryan said. No, she said, that was not a 17th-century practice.

Neither are the Popsicles that supervisors brought to the outdoor museum during one recent spell of 100-degree days.

"I didn't know about those!" said Ashley Crawmer, an eighth-grader who is earning class credit as a volunteer interpreter. She was dressed like the adults yesterday, sitting quietly at the table in the kitchen, threading beads in a rosary.

All this summer sweat is hard on clothes, said costume curator Jean Robinson, who was dressed in a smart and cool white cotton tunic--one layer--and basking in the cool blast of a window air conditioner in her workshop, a world and centuries away from the make-believe plantation and the museum's replica 17th-century vessel, the Dove.

Sweat has salt and acid, and those things are hard on any fabric, Robinson said. The sun fades the color on the woolen doublets of the men on the ship. At the end of the summer season, all the outfits are returned to her, and Robinson said she gets down to business of cleaning and repair.

The way interpreter Eileen Sherman sees it, being hot in a period costume is the price of an authentic portrayal of Colonial life. She confessed to some impatience with visitors who insist on remarking on how hot she must be.

"If people did it 300 years ago, I think we can do it nowadays. It was just normal then, and I think we have gotten soft," Sherman said.

CAPTION: As temperatures topped 100 degrees, Jessica Crawmer, 10, and her sister Ashley, 13, in 17th-century clothing, soak their feet in cold water to stay cool.

CAPTION: Jessica Crawmer, 10, pours water from her gourd to cool off. The costumed interpreters in St. Mary's City try to be authentic for visitors, and officials at the living museum ensure they are also safe in the heat.

CAPTION: Eileen Sherman mops her brow as she and Heather Loeffler work in the field. Sherman says being hot is the price of an authentic portrayal.