Democrat Michael Dukakis charged in a tough new TV ad Friday that George Bush is airing commercials that are "full of lies and he knows it." Bush, leading in the polls, turned to a condemnation of chemical weapons.

Trailing with just 17 days remaining until the election, the Dukakis campaign unveiled its most pointed ads of the year, accusing Bush of distorting Dukakis' record on crime and defense.The Massachusetts governor set the stage earlier Friday when he said on network talk shows, "I've been subject to attacks and distortions" and the "American people are not happy with this campaign" because it had been too negative.

He said Bush's attack on the Massachusetts prisoner-furlough program was "cynical and very hypocritical." The Bush camp has made much of the fact that Willie Horton, a convicted murderer, escaped while on furlough, raped a Maryland woman and assaulted her fiance.

"To play politics with that kind of human tragedy, I think, is one of the most cynical things you can do," Dukakis said.

In one of the new TV spots, Dukakis is shown watching a Bush campaign ad depicting Dukakis riding in an armored tank. Dukakis snaps off the TV, turns to the viewer and says he is "fed up" with Bush's attacks.

"Haven't seen anything like it in 25 years of public life, George Bush's negative TV ads: distorting my record, full of lies and he knows it," Dukakis says in his own ad.

He accuses Bush of "dragging truth into the gutter" and adds: "I'm on the record for the very weapons systems his ads say I'm against."

Sig Rogich, Bush's ad director, defended the Republican's commercials, saying, "There's nothing erroneous about any of those ads or the truth of the matter is the networks wouldn't accept them. . . . We stand by everything . . . in our ads."

The Republicans were on the attack, too.

Bush, seeking Ohio's 23 electoral votes, said Dukakis' opposition to the space-based missile defense system, known as "Star Wars," was bad for the country.

In the main thrust of his speech, Bush said he wants to be known as the president who helped achieve an effective ban on chemical weapons, a subject he said had gained new urgency with their recent use in the Iran-Iraq war.

The Dukakis campaign has accused Bush of being hypocritical on the chemical warfare issue since he cast tie-breaking votes in the Senate to continue stockpiling new germ and chemical weapons in 1983 and 1986. But a Bush aide said the Reagan administration felt it was better to put the old deteriorating U.S. chemical weapons in new, safer forms.