GOV. James R. Thompson (R), 42, is cruising to reelection over state Comptroller Michael J. Bakalis (D), 40, with the likely margin large enough to sustain - if not magnify - Thompson's presidential ambitions. Today's Chicago Sun Times poll gives Thompson a 62-to-38 percent lead.

Real attention focuses on the Senate contest, where the "negative" ads used by conservative challenger Alex Seith (D), 44, a Chicago lawyer, to undermine Sen. Charles H. Percy (R), 59, have themselves become the major issue in the closing days of the campaign. In the last four days, Percy has gained a point a day in the Sun-Times continuing polling, and today Seith's margin was less than 1 point. If the trend continues, Percy may pull it out.

In House races, perenially endangered Rep. Abner J. Mikva (D) is in another cliff-hanger, this time against state Rep. John E. Porter (R). In the 22nd District race that has been covered in a Washington Post series, dentist Daniel B. Crane (R), brother of presidential hopeful Rep. Philip M. Crane (R-Ill.), remains a slight favorite to defeat state Sen. Terry L. Bruce (D). The district has been Democratic, so a turnover is possible.