Approximately 3500 students are expected to register for the Harvard Summer School by the time registration ends tonight, Marshall R. Pihl '55, associate director of the Summer School, said yesterday. If this estimate proves correct, enrollment will be up about 25 per cent from last summer.

Long lines and an array of forms and handouts greeted the arriving students, who traveled to Harvard from across the U.S. or from 70 foreign countries.

Summer School officials estimate that about 500, or 15 per cent, of this year's Summer School students will be Harvard students, 15 per cent will be foreign students, 22 per cent secondary school students, and the rest college or graduate students. All enrollment figures are approximate because of the school's open admissions policy, which allows any graduate of an accredited secondary school who can pay the $375-per-course fee to walk in and register. Classes start today, although registration continues until 8 p.m. tonight.

For the first time in years, Chemistry S-20, "Organic Chemistry," is not the school's most popular course. Preliminary enrollment figures show "English as a Foreign Language" leading the list with 200 students and Chem 20 close behind with 177 registered, Fred Yalouris, registrar of the Summer School, said yesterday.

Chemistry S-1, "Introductory and Inorganic Chemistry," places third this summer with 146 students, up from 126 last year, he added. But the most dramatic increase in enrollment came in Elementary Chinese with eight students last year and 54 this summer, Yalouris said.

This summer marks the fourth year the school has recruited secondary school students, a move taken to offset a decline in enrollment dating back to the early '70s. Michael Shinagel, director of the Summer School, said he expects over 550 secondary school students to attend the school this summer. By far the largest groups of students come from New York, California, Massachusetts and New Jersey, but the group includes eight students from Iran, as well as students from Japan, Nicaragua, Greece, Italy, Korea, China, Taiwan, France, Venezuela, Canada and other countries.

The school recruits high school students with high PSAT's using the Educational Testing Service's profiles of students who have taken the test. The profiles break students down into groups by geographical area. PSAT test scores, grade point averages, and potential career choices. The school selects about 20,000 students from the one million on the list for direct-mailing recruitment, Pihl said Friday.

All secondary school students must fill out essay application forms, including two recommendations from teachers and principal or headmaster.

Bohemian?

One secondary school student, Rebecca Dolinsky of New York City, said yesterday she came to the school to study art because her own school, Brearley, is very pressured academically, and she "wanted to see if I could lead the life of an artist and survive."

For Dolinsky as for other secondary school students, however, the main attraction seems to be Harvard itself-and the eventual possibility of entering here.

"Like any American influenced by the society I live in, there's no way I'm not going to be swept away by the beauty of Harvard," Dolinsky says. And Deborah Cobb, a student from Cambridge Roxbury School, says simply, "I'd love to come to Harvard-if I'm accepted.