WASHINGTON — As summer vacation season kicked in, Americans got out of their cars, driving 12.2 billion fewer miles in June than the same month a year earlier.

The 4.7 percent decline, which came while gas prices were peaking, was the biggest monthly driving drop in a downward trend that began in November, the Federal Highway Administration said yesterday.

"Clearly, more Americans chose to stay close to home in June than in previous years," said Transportation Secretary Mary Peters.

Overall, Americans drove 53.2 billion fewer miles from November through June than they did over the same eight-month period a year earlier, according to the highway agency's latest monthly report on driving. That's a larger decline than the 49.3 billion fewer miles driven by Americans over the entire decade of the 1970s, a period marked by oil embargoes and gas lines, the agency said.

Travel Industry Association spokeswoman Cathy Keefe said the June driving decline "is not surprising, given the environment that we were in." But she was optimistic that the recent drop in gas prices to below $4 a gallon in many parts of the country will have travelers on the road again.

"I think people have started to take the increase in gas prices somewhat more in stride," Keefe said. The trade association is predicting only a 1.2 percent decline in all forms of business and leisure travel this year.

Some of the biggest declines in June compared with a year ago were in such popular vacation states as Maine, down 7 percent, and Florida, down 6 percent. Western states with wide-open spaces were also part of the trend — down 7.7 percent in Montana, 6.9 percent in Washington, 6.8 percent in Wyoming, 6.7 percent in Nevada, 6.2 percent in Kansas and 6.1 percent in Alaska.

In Hawai'i, the decline was 3.4 percent.

Gas consumption was down, too. The highway administration said motorists consumed 400 million fewer gallons of gasoline and 318 million fewer gallons of diesel in the first quarter of 2008 than in the same period in 2007.

Peters said the decline in driving will mean less money for highway repairs and construction projects needed to relieve traffic congestion.

The Highway Trust Fund, which underwrites the projects, is funded by the federal 18.4 cents a gallon tax on gasoline and 24.4 cents a gallon tax on diesel.