If high school students want to start summer jobs when school's out, they ought to start looking now -- even though many businesses that hire seasonally already have done so.

The Center for Labor Market Studies based at Northeastern University predicts that summer employment for high school students will fall to its lowest level since World War II.

"The teens that get the jobs this summer are going to be the ones who are looking now," said Joel McLaughlin, a research assistant at the center.

Last year, 34.5 percent of the population ages 16 to 19 were working, the lowest level in 60 years, but this year the center is predicting that will drop to 34 percent.

The big retailers won't hire anyone under 18, Mr. McLaughlin said, which leaves the smaller businesses, many of which already have hired their summer help.

LeeAnne Ciotti, the manager of the Ritas Italian Water Ice in Robinson, said their "help wanted" sign went up in February and they currently have 10 employees, eight of whom are in high school. Another five members of the crew this summer will be college students -- one has started working there and four more are due to start soon.

For those who don't get a job right away, Kennywood and Sandcastle always are looking for young workers, particularly in the fall, said Mary Lou Rosemeyer, the spokeswoman for Kennywood. She said high school students were usually needed in the fall because the college students have to leave, but that that sets up the younger employees for a job the next summer.

"We retain almost 70 percent of our people," she said. "The majority of our people are students."