TAMPA, Fla. — The 2008 Atlantic hurricane season could be slightly busier than average, with a good chance of six to nine hurricanes forming, federal forecasters said yesterday in a new way of making predictions.

National Oceanic and Atmospheric Administration officials also said 12 to 16 named storms and two to five major hurricanes could form.

They said there is only a 60% to 70% chance for their predictions to come true, the first time officials gave a probability. They took that step following years of criticism of their long range forecasts, which have usually been fairly accurate but in some cases have been way off.

For example, government forecasters expected between 12 and 15 named storms in 2005, but there turned out to be 28, the busiest season on record.

Forecasters stress that residents should always be prepared no matter what the seasonal forecasts say, because even a slow season can be disastrous. The government’s seasonal forecasts don’t predict whether, where, or when any of these storms may hit land.

The agency’s lead forecaster for Atlantic hurricanes, Gerry Bell, said probabilities were included because people had come to rely too much on the forecasts. “Basically it was interpreted as a 100% chance,” he said.

An average season has 11 named storms, including six hurricanes of which two reach major status with winds of more than 110 mph. This year should be about average or slightly more active, forecasters said.

Forecasters and emergency responders fear that coastal residents will be apathetic this year after America escaped the past two storm seasons virtually unscathed.

“Living in a coastal state means having a plan for each and every hurricane season. Review or complete emergency plans now — before a storm threatens,” an NOAA administrator, Conrad C. Lautenbacher, said. “Planning and preparation is the key to storm survival and recovery.”

A Colorado State University weather researcher, William Gray, expects 15 named storms, eight hurricanes and four major this year.

Last year, there were 15 named storms and six hurricanes, two of which were major. The government predicted between 13 and 17 named storms, seven to 10 hurricanes, and three to five major hurricanes.

Gray was further off the mark. Before the start of the season, he forecast 17 named storms, including nine hurricanes, five of them major.

The Atlantic season begins June 1 and runs through November 30.