Chicago ? Summer’s almost here and that means teens will have more time on their hands to pick up bad habits — such as smoking marijuana and drinking alcohol, a new federal survey says.

The National Survey on Drug Use and Health found that June and July were the most popular time for teens to try marijuana, with about 6,300 new users a day during those months. That compares with about 4,700 new users a day during other times of the year.

Additionally, the survey found that first-time use of alcohol and cigarettes also increases during the summer, when many teens are less supervised and, particularly in this economy, having trouble finding jobs. First-time alcohol use also peaks in December and January. The 2002 survey included 68,000 youths 12 or older.

At a Friday news conference in Chicago, White House drug czar John Walters challenged teens and parents to quell marijuana use this summer, noting that the drug has been developed to become much more potent and addictive in the past 20 years.

“You are going to be on the front line of those influences,” said Walters, addressing a group of Chicago high school students. “But we need adults to stand with you.”

Maribel Davila, a high school freshman in attendance, also placed responsibility on parents.

“A lot of kids are pushed because there’s a lot of stuff going on at home,” she said, referring to such factors as divorce, adults’ own addiction issues and other family discord.

None of the students were surprised by the findings. Nor was at least one researcher not involved with the survey.

While its helpful to know when young people are most likely to start taking drugs “the real question is ‘What should they do based on that information?”‘ said Lloyd Johnston, who heads the University of Michigan’s Institute for Social Research.

Walters agreed with Johnston that the best way to deter marijuana use is not just to say “Don’t do drugs.”

To that end, federal officials have begun running ads directed at teens that urge them to take a stand with friends who use marijuana and other drugs.

The government has also begun a campaign that maps out basic tactics for parents such as setting rules, monitoring a teen’s activity and scheduling family time.