Ever since John F. Kennedy '40 abandoned his safe House seat to run for the U.S. Senate in 1952, THOMAS P. O'NEILL Jr. (D-Mass.) has represented Cambridge, along with Boston's Back Bay and parts of several other neighboring cities in Massachusetts's 18th Congressional district. By virtue of his position as Speaker of the House, his popularity throughout the district, and the overwhelmingly Democratic voter registration, "Tip" O'Neill can't possibly lose to perennial Republican challenger William "Battlin' Bill" Barnstead tomorrow.

The races for House seats vacated by Rep. Paul E. Tsongas (D-Mass.) and Michael J. Harrington '58 (D-Mass.), are different. Lawrence attorney James M. Shannon survived a brutal five-man primary fight in the Fifth District and as the Democratic nominee is an odds-on favorite to succeed Tsongas. His Republican opponent, Middlesex County Sheriff John Buckley, has been running strong, but observers doubt his votes in Boston's northwest suburbs will offset Shannon's expected power in the Democratic stronghold cities of Lowell and Lawrence.

In the Sixth District, Peabody Mayor Nicholas Mavroules, the easy winner of a three-man Democratic primary, is likewise expected to make Republican airline pilot William Bronson a two-time loser tomorrow (Bronson ran for the seat in 1976, and gave Harrington a scare that some say was a factor in his decision not to run for re-election last June.). The Sixth, while the home of Yankees like Frank Hatch, beautiful beaches and country clubs, is also the home of dying cities like Lynn and Haverhill, and so is likely to remain in the Democratic column.

Should either the Fifth or Sixth go Republican, the government professors will go scurrying for their election statistics. But if Tip's district goes Republican, the resulting scramble should bring down the House.