The four US airlines jockeying for the next route to China are accelerating their campaigns to win support for their applications from the public and businesses.

AMR Corp.'s American Airlines, UAL Corp.'s United Airlines, Continental Airlines and Northwest Airlines are all racing to secure the prestigious service to add to their Asia routes.

As they make their case to the Transportation Department, which awards the route, the airlines also are making their case to potential customers.

"This is not some normal route application. China is where it's at," airline consultant Michael Boyd said. "It's critical because airlines that have the best access to China are going to have the best revenue flows domestically and internationally."

U.S. carriers, battered by low-cost competition at home, have sought out growth on lucrative international routes, and China's economic expansion presents a strong opportunity for airlines with service there.

The Transportation Department has said it would grant one additional daily route to China to one of four U.S. airlines that already fly there. The application deadline was in August, and the government is due to make its choice in February.

The United States keeps tight reins on rights to fly to China, so competition for the route among airlines is stiff.

United, which wants to add service from Washington D.C. to Beijing, is a member of the Capital-to-Capital Coalition, a group of Washington, D.C. organizations that supports that route. Currently there is no service between the two capitals.

"This is a unique route case for United, as it closes that service gap and provides much-needed capital-to-capital connectivity for our customers, governments, commerce and culture," UAL Chief Executive Glenn Tilton said in a recorded message to employees on Tuesday.

Continental jumped into the public relations contest last week, staging a press conference in New York's Chinatown, where it asked supporters to lobby for the airline's proposed service between New York/Newark and Shanghai.

The carrier has received more than 15,000 letters supporting its application, spokeswoman Julie King said.

American, which hopes to add service between Dallas/Fort Worth and Beijing, launched a Web site last month to win public support. The site, flytochinaonaa.com, calls on businesses and community members to speak out in favor of the route.

Northwest said it plans to launch a Web site to support its proposed Detroit-to-Shanghai route. In the meantime, it is making its case in briefings to customers and airport officials.

A strong public relations campaign could make or break an airline's bid to win the new route, said Joe Schwieterman, a transportation expert at DePaul University.

He said the public is unlikely to get excited over a new China route, but the airline that wins the most support from businesses has a leg up on the competition.

"Commerce speaks loudest when it comes to choosing new routes to China," Schwieterman said. "This is a horse race that is hard to predict."