ATLANTA (AP) - America's schools are doing a better job of warning students off of tobacco, but many scale back the message when it's needed most, a new government survey says.

The survey conducted last year shows nearly two-thirds of public schools prohibit all forms of tobacco on school property and at off-campus school functions - up from just 36 percent in 1994.

But fewer schools teach health education as students get older, when they are more likely to be exposed to tobacco and alcohol. More than a quarter of schools teach health to sixth-graders, but just 2 percent teach it to high school seniors.

"It's during these high school years that kids are practicing most of these health-risk behaviors," said Dr. Laura Kann, the chief researcher for the study.

The survey, the government's most comprehensive study of school health programs, was released Wednesday by the U.S. Centers for Disease Control and Prevention.

Health officials hope it will be a road map to help schools and districts understand the areas that need the most attention.

One particularly encouraging finding: The nation's schools are steadily increasing programs to stop violence.

Almost three-fourths of middle and high schools teach violence-prevention to students, and almost 90 percent of U.S. states offer training for educators on how to teach violence prevention. Both numbers are significant jumps from 1994, likely because of the spate of high-profile, deadly school shootings in the late 1990s.

"That's a logical conclusion to jump to," Kann said. "We've had some pretty horrific events in schools since 1994."

The report also gives federal health officials fresh numbers to back up a complaint they've had for years: While school-sponsored lunches remain mostly healthy, too many schools are loading up on vending machines that dish out high-fat snacks and sugary soft drinks.

Nearly 75 percent of middle schools and 98 percent of high schools have vending machines with those unhealthy snacks, the CDC said.

Even when students wash all that down with school-ordered milk, almost two-thirds of it is high in fat, the survey said.

Among other findings in the survey, conducted in the spring of 2000 among districts and schools in all 50 states:

-Schools require less physical education as students get older. Half of schools require P.E. in first through fifth grades, but just 6 percent require it daily of high school seniors. About half of schools have intramural sports or physical-activity clubs.

-Two-thirds of schools offer programs for mental health and social services, and more than three-fourths provide crisis intervention for physical, sexual and emotional abuse.

-Almost all schools have policies banning drug use, fighting, carrying weapons and harassment of other students.

Copyright 2001 The Associated Press. All rights reserved.