A new Mets minor league stadium in Coney Island could cost almost 30 percent more than had been planned, according to figures city officials released during the stadium's groundbreaking yesterday.

In order to complete it by next June, the city may spend up to $39 million to build the 6,500-seat stadium instead of $30 million, officials said.

Mayor Rudolph Giuliani said the increase was necessary "to get it done on time."

The city hopes to have simultaneous opening days for the Mets team, now in Pittsfield, Mass., and the Yankees' farm team, which will be housed in a new stadium on Staten Island, which is costing $76 million, including neighborhood improvements.

Bruce Brodoff, spokesman for the city's Economic Development Corporation, said the city had hoped to complete the Coney Island stadium by 2001 but had also discussed stretching the project to 2002.

But the city determined that doing it over two years would actually cost more than getting it done by next June.

Critics say it is too much money for baseball.

"These are ridiculous prices to pay for low minor-league stadiums," said Councilman John Sabini (D-Jackson Heights), who voted for the stadium but is worried about the cost.

Giuliani believes the stadium's benefits outweigh the costs, because it will attract crowds.

"That's the way you bring people back to Coney Island," Giuliani said. "They're not coming here now."

Coney Island civic leaders say they are glad to have the stadium but hope it translates into jobs for local residents.

Cynthia Sanchez, co-chairwoman of the Coney Island Volunteer Information Cooperative, said men and women in the community congregate every morning at 6:30 a.m. against the fence that lines the site of the stadium.

"Every morning they are standing there faithfully looking for jobs," she said. "But so far, they have not yet been fulfilled."

The city has promised 700 new jobs for the yearlong construction. So far, only six residents have been hired, Brodoff said.

Brodoff said he is confident Turner Construction will hire more local people once more work begins, such as the plumbing and landscaping phases.

In addition to the cost of the stadium, the city will spend approximately $30 million to build parking areas and an adjacent Little League field and to spruce up the boardwalk.