Sen. Mark O. Hatfield (R-Ore.) is learning the hard way about the anti-incumbency sentiment of voters this election cycle. His reelection, once viewed as easy, is in jeopardy.

A poll released yesterday showed Hatfield, who had a 36-percentage-point lead over Democratic challenger Harry Lonsdale in August, trailing by six points, 50 to 44 percent.

Oregon pollster Tim Hibbits, who conducted the poll for KATU-TV in Portland, called the results "an indication of the tidal wave of anti-incumbency feeling that is sweeping over this state and this particular race." Lonsdale's television ads have pumped the message that it is time for a change.

Hatfield, who had been running a low-key campaign until a poll two weeks ago showed him ahead by only six points, rushed back to the state and began an aggressive and negative campaign against Lonsdale, a political newcomer.

"The immediate message is that Mark Hatfield's negative campaign has backfired," said Lonsdale spokesman Dan Walters. "None of the voters have ever seen this Mark Hatfield. This is not the statesman

they knew, and they don't like it."

Hatfield aide Bill Calder said, "We need to better define Harry Lonsdale -- that he represents a dangerous choice and that Mark Hatfield is the appropriate choice." Noting that Hatfield often is a party maverick, Calder added, "What hasn't been clear to the voters is that Mark Hatfield represents many of the anti-incumbency sentiments they feel."

Walters said he expects the race "to see-saw right to the end." He said Lonsdale "will keep the pressure on Hatfield and will keep sending our message that voters are tired of politics as usual." While Lonsdale has not made abortion an issue (he supports abortion rights; Hatfield does not), "it is lurking out there and may end up being the decisive issue," Walters said.