CLEAR LAKE, Iowa — Senator Clinton suggested yesterday that Senator Obama has too little experience and perhaps too much ambition, pressing an increasingly aggressive campaign against her chief rival for the Democratic presidential nomination.

Both candidates were in Iowa, one month before the nation’s leadoff caucuses with new polls showing Mr. Obama had whittled away her early lead and they were virtually tied among Democrats in the state.

“So you decide which makes more sense: Entrust our country to someone who is ready on day one … or to put America in the hands of someone with little national or international experience, who started running for president the day he arrived in the U.S. Senate,” Mrs. Clinton said.

For the second day in a row, the New York senator and former first lady turned up the heat in her race with the Illinois senator.

Her rhetoric — and countercharges from Mr. Obama — underscored the tightness of a race in which polls show a dead heat between them, with a former senator, John Edwards of North Carolina, also in strong contention. Many Iowa caucus goers say they still haven’t made up their minds or could yet change them.

Mrs. Clinton accused Mr. Obama of a “rush to campaign” in not returning to Washington this fall to vote on a resolution naming an Iranian military unit a terrorist organization. The Bush administration supported the measure, as did Mrs. Clinton — and Mr. Obama has criticized her for it.

“Presidents can’t dodge the tough political fights,” she said.

Mr. Obama spokesman Bill Burton retorted, “The truth is, Barack Obama doesn’t need lectures in political courage from someone who followed George Bush to war in Iraq, gave him the benefit of the doubt on Iran, supported NAFTA, and opposed ethanol until she decided to run for president.”

Meanwhile, liberal activists plan to begin airing a television ad against Mrs. Clinton in Iowa this week, the first non-Republican negative ad aimed at a Democratic presidential candidate. Democratic Courage, has accused Mrs. Clinton of making policy decisions on the basis of polls, not convictions. It planned to introduce the ad today. The group’s president, Glenn Hurowitz, described the spot as a modest buy that would run on cable only, meaning it won’t be seen as much as ads by Mrs. Clinton and Mr. Obama, who are spending hundreds of thousands of dollars on ads in the state.

Democratic Courage is a political action committee, financed by contributions of no more than $5,000 a person.

“We are concerned that she wouldn’t be the best candidate in the general election or the best president because she is so easily bullied by the Republican attack machine,” Mr. Hurowitz said.

In related news, the man accused of taking hostages at a Clinton campaign office last week watched impassively during his video arraignment yesterday as he was portrayed alternatively as a sick man desperately seeking psychiatric help and a manipulative longtime criminal.

The judge ordered Leeland Eisenberg held on $500,000 cash bail on six felony charges and ordered a psychiatric evaluation for him. “I think it’s very, very important, to keep this man under lock and key for now until we get to the bottom of his mental health problems,” Rochester District Court Judge Daniel Cappiello said.

Prosecutor Janice Rundles asked for the high bail, saying Eisenberg, 46, has two rape convictions and would be a threat to the public.