When the National Crime Prevention Council made plans to bring its annual convention to the Washington area, it could have chosen any one of the city's major hotels. But the council, as many other groups are doing, picked a Crystal City hotel in Arlington.

"Arlington is a good blend for people from all areas," said Gwen Hall, a council official and Washington resident. "We wouldn't want to expose people from rural areas to the things those of us who live here go through everyday," she said, citing transportation, crime and parking problems.

With 30 hotels open and seven more planned, Arlington is making a determined bid for a major share of the multimillion dollar Washington convention business, a market that the District used to have to itself.

The county says it now has one out of every five hotel rooms in the area and is using them to mount a challenge for the convention trade with a campaign that stresses lower room rates, easy transportation to the area's major tourist attractions and what Arlington boosters say is a nearby escape from the District's high crime rate.

Even so, Arlington is using many of Washington's assets to lure conventions and visitors. The county's travel slogan since 1977 has been "Arlington: The Washington Connection." In one brochure, titled "Arlington Virginia Overlooking Washington, D.C." most of the color photographs are of attractions in the District.

Arlington, says Robert Gratton, chairman of the county Visitors Commission, is winning conventions away from Washington "every day. . . . The hotels of Arlington are now an intricate part of the hotel business in the area, so that people now think of Arlington when they're looking for a hotel, not just Northwest Washington."

Austin Kenny, head of the Washington Convention and Visitors Association, tends to dismiss Arlington as a direct competitor. Washington's competition is not with Arlington, he said, it is with larger cities such as New York and San Francisco. "I don't look at it as competition between the two areas, Kenny said, "but between the hotels in the two areas."

The Arlington hotel boom, helped by the proximity of the Pentagon and National Airport, is on an increase shared by other area suburban jurisdictions and shows no sign of slackening. The 454-room Marriott Gateway and the a 688-room Hyatt Regency, opened last year. Another Crystal City hotel, the Sheraton Crystal Gateway, with 197 rooms, is scheduled to open this month.

A spokesman from the California-based Hyatt Hotel chain said that Hyatt and other hotel chains are building in the Washington suburbs because of the new businesses there and the arrival of Metro. "You have a rapid expansion of business in the suburbs," said Rick Fowler, the Hyatt spokesman. "The Tysons Corner area is like the Silicon Valley of the East."

An economic development official in Fairfax County, where Tysons is located, said that the county has 44 hotels and seven more are planned or under construction. Montgomery County, an official said, added four hotels to its 25 in the past two years, gaining more than 1,000 rooms and another large hotel is under construction there. Prince George's County has 32 hotels and seven more under construction.

The District is undergoing its own hotel surge, thanks to the opening of the new D.C. Convention Center. About 6,000 new rooms in 12 new hotels have been or soon will be opened in the city, raising some fears in the industry that Washington itself may soon be overbuilt.

One advantage the convention goers find in the suburbs is price. A spokesman for the Marriott Hotel chain said that the typical single at their Gaithersburg hotel would cost $44 to $76 while a single at the chain's 22nd Street hotel would be $85 to $130.

Arlington's Gratton said the hotel industry is helping to account for the large increase in tax revenues that Arlington is securing from tourists. In 1979, he said, it is estimated that tourists spent $256 million in Arlington. This year it is estimated that tourists will spend more than $500 million, he said.

To keep the tourists coming, the county last year mailed nearly 140,000 brochures to travel agents, tour planners and convention organizers around the nation and Canada. "Our goal is to enhance Arlington's image when people think of the Washington area," said Francine Bradshaw of the Arlington Visitors Commission.