KOBE -- Nearly 30 years after it was first proposed, construction of the controversial Kobe airport officially began Monday morning off Port Island amid protests and doubts about its economic feasibility.

The single-runway airport will be built at a cost of 310 billion yen on an artificial island. Scheduled to open in 2005, it will be the third airport covering the Kansai region.

At 8 a.m. Monday, vessels began setting up a large curtain around the reclamation site to prevent pollution from leaking into the surrounding bay, as about a half dozen protesters demonstrated on a yacht near the site.

After the curtain is set up around the 272-hectare site, a retaining wall will be built with 24 million cu. meters of sand and rocks.

The entire wall is expected to be completed in fall 2002, and the landfill operation for the artificial island will commence in 2001. About 66 million cu. meters of sand and dirt will be required.

Kobe Mayor Kazutoshi Sasayama, who has supported the project since the early 1990s, said Monday that the airport would ensure Kobe's economic future.

"We have to create a city that attracts new industries, especially information technology. Having an airport will lead to economic revitalization," he said.

The history of the Kobe airport project dates to the mid-1960s, when the Transportation Ministry announced plans for a new international airport in the Kansai region. During the 1970s, Osaka and Kobe battled fiercely to be chosen as the site.

In 1982, the ministry chose the bay off southern Osaka Prefecture as the location for Kansai International Airport, and Kobe was forced to resubmit plans for a local airport.

While the Kobe airport won official approval as a domestic-only facility, some local politicians remain hopeful that it can attract international flights.

However, doubt is widespread within the aviation industry over whether Kansai really needs another airport, with Osaka airport covering domestic flights and a struggling Kansai International steadily losing carriers.

While Kobe estimates that 3.4 million people will use the new airport annually, industry watchers say the forecast is too optimistic because the Kansai and Osaka airports still have surplus capacity.

Throughout the 1970s and 1980s, local public support for a Kobe airport was mixed. Following the 1995 earthquake, opposition grew stronger, as many felt that fiscally strained Kobe should spend money to cover the needs of the quake survivors instead.

Last fall, 350,000 people, including 310,000 registered Kobe city voters, or one-third of the total, signed a petition requesting a plebiscite on the issue. Media opinion polls showed between 70 percent and 80 percent of Kobe residents opposed the project. But in December, the municipal assembly, which supports the airport by nearly a two-thirds majority, rejected the petition.

Although construction has finally begun, opponents have vowed to continue their battle, both directly and indirectly.

"We will continue to protest until the airport is stopped," said Makoto Okamoto, a member of a local citizens' group.

Opponents plan three separate approaches. Okamoto's group plans to file lawsuits with the Kobe District Court to stop construction on financial and environmental grounds. The 21 municipal assembly members opposing the airport are discussing the possibility of reviving the plebiscite campaign later this year. Another citizens' group is conducting a campaign to recall the mayor.

Official construction costs are estimated at 310 billion yen, which will be paid for primarily with local bonds and the planned sale of land on the airport island to the private sector. But this estimate does not cover the cost of constructing transportation networks to provide access to the site. Privately, city officials say that when a new subway line is built, the total cost could top 1 trillion yen.

The mayor, however, insisted that cost overruns were unlikely.

"We intend to keep costs at the stated figure of about 310 billion yen," Sasayama said.