The outdoors is in.

And that's what the Prince William County-Manassas Conference and Visitors Bureau is banking on.

For nearly two years, the bureau has promoted the great outdoors as a great enticement for visitors.

"The outdoor product is relatively new," said Sharon Cavileer, spokeswoman for the bureau. "Within the last year and a half, we have promoted it more heavily."

And with good reason, she said. What many would-be visitors might not realize is that the Prince William area offers a "wildly expansive outdoor product for both tourists and residents of Washington," Cavileer said. "We offer the region prime outdoor activities."

The marketing for areas outside the District often has been tricky. What used to seem like a negative aspect to the outer counties -- a wide-open expanse of "countryside" -- has become a major draw for city folk and out-of-town tourists alike. The ecotourism trend has become a major asset to the county, and visiting places such as Prince William is quickly becoming typical weekend routine for SUV-driving District residents looking for a place to bike, hike, camp and otherwise get out of town easily.

Prince William touts itself as one of the top 10 places to bass fish in the United States. It also bills itself as a great place to camp and hike -- part of the Appalachian Trail runs through the county -- and a prime spot to boat, canoe and raft, among other things.

Officials don't know exactly how many visitors come to Prince William for outdoor activities. But there seems to have been an obvious swell, officials say. Much of that might be because of the burgeoning interest in outdoor activities.

Russ Whitlock, Prince William Forest Park supervisor ranger, said there has been a marked increase in visitors who mountain bike.

"One of the biggest increases is the increase in bicycle use. Especially the all-terrain bike," he said. "The county . . . has gotten a lot of calls looking for places for mountain biking.

"The only thing I know is that our telephone and Internet requests are up. The road rangers are observing more" bikers, campers and hikers, Whitlock said. About a quarter-million people visit the park each year, he said.

The area is vying for tourists and visitors who can increase interest and business in the county. The park, with 16 miles of bicycle trails and off-road biking on any of its 10 fire roads, is part of that plan.

Visitors to Prince William Forest Park brought $2.5 million to the county in 1996, Whitlock said. Visitors pay $4 per vehicle, good for three days, or $15 for an annual pass. Camping fees vary from $10 to $30 per night, per camp site.

"Visitors are surprised with the beauty, topography, how close it is to everything else," said Cavileer. And luring visitors to the area increases interest in the county and income to area businesses, she said. "There isn't a fisherman that doesn't buy gas, beer, need a place to stay or outdoor equipment."

Whether this ecotourism is actually benefiting the county and its economic development is a question many people say must be studied further. Bill Vaughan, research manager for the Prince William County Department of Economic Development, said this kind of ecotourism enhances the county's image, and thus will contribute to economic development.

More visitors for outdoor recreation could mean more interest in the county and could help the Economic Development Department in its focus: luring target industries -- high-technology and bio-research -- to relocate to the county.

Tourism in Prince William, which falls under the Parks and Recreation Department, will receive $1.02 million from the county for fiscal 2000, said Kathy Bentz, county communications director. Bentz said she knows of no specific numbers that measure the financial effect of tourism on the county.

Still, the effect is great. Potomac Mills Mall has long been one of of the top tourist draws in the state, and the Manassas National Battlefield Park receives thousands of visitors annually. Local golf courses, both publicly and privately owned, attract still more people. And the Occoquan Bay National Wildlife Refuge, which opened last year, is drawing new visitors.

A group formed to study tourism in the county will issue a report around August, Bentz said. The study might suggest, among other things, making tourism a department of its own. Bentz said that tourism spending is increasing rapidly and that tourism will continue to become very important to Prince William.

The report will be a study of whether the county is achieving what it needs to achieve through tourism and what it needs to improve, she said. It also will recommend ways to measure the effect of tourism on the county.

That result of that study could mean more money for increased advertising, educational programs and general spending on attractions.

The Board of County Supervisors compiled a strategic plan, which named major strategies for tourism. Among those was the need to promote Prince William tourist attractions.

In the meantime, area parks are enjoying the recent influx of visitors. "Part of it is people's awareness that they're discovering this park now," said Whitlock. "People are getting more outdoor oriented and are looking for these opportunities close to the city."

CAPTION: Debbie Loew and her children take a mini-vacation at Prince William Forest Park. The family, formerly of Manassas, has been in Ireland for two years. About a quarter-million people visit the park each year. The Prince William County-Manassas Conference and Visitors Bureau has been promoting the great outdoors as a great enticement for visitors.