In the wake of last Tuesday's Illinois primary, which saw four incumbents squeezed out of the House delegation, both parties are on the prowl for more targets.

Democrats see a chance in the 17th District, where state Sen. Kenneth McMillan (R) defeated Rep. Tom Railsback (R) in a close primary, but they still have an uphill struggle. McMillan, though lacking the labor support in Rock Island County that Railsback enjoyed, put together a strong organization in the rural areas that dominate the rest of the district. The Democratic nominee, 30-year-old attorney Lane Evans, is untested as a campaigner.

The Democrats may have a better chance against 22-year veteran Paul Findley (R), whose district has been redrawn to include much more Democratic territory. Richard J. Durbin (D), who once ran for lieutenant governor, rolled up a good margin over his opponent in the primary.

On the GOP side, there is more than normal enthusiasm about the campaign against Rep. Sidney R. Yates (D), who has been in Congress since 1948 with a two-year break in the 1960s for a losing Senate bid. Catherine Bertini, the GOP candidate, is drawing support from women's groups and corporations.