Summer jobs averaging $45 a week are open to juniors and seniors who want to work with the Civil Service's Students Aid Program, the Student Placement Office announced yesterday. Only catch in the deal comes early this month in the form of a standard examination.

The Student Aid Program, initiated last year, places qualified undergraduates in temporary appointments in engineering (civil, electrical, and mechanical), chemistry, physics, mathematics, metallurgy, naval architecture, and psychology. Last year the program handled 58 students from 17 New England colleges.

Of the men who were given Student Aid appointments last summer, 52 have asked to return this year, the office reported. Places of occupation, all in New England, include the Watertown Arsenal, the U. S. Navy Underwater Sound Laboratory at New London, Connecticut, and other government stations.

Applications for the general examination, which closes January 20, must be made to the Civil Service regional office in Boston.