OTTUMWA, IOWA, JAN. 16 -- Bill and Mary Kai Nelson, longtime Democratic Party activists, were ready to give Gary Hart a second chance. They had watched all the Hart coverage on network television and had begun to think that he might have the "ideas" and "charisma" to capture the nomination.

But the Nelsons abruptly changed their minds last night after watching Hart debate his six Democratic rivals for the first time since reentering the presidential race last month.

The first question of the debate, televised statewide from Des Moines, did it for Bill Nelson. It was about a Hart statement that he would "not be the first adulterer in the White House."

"When I heard the question, I realized he would be crippled all the way by the Donna Rice thing," said Bill Nelson, a 45-year-old architect. "I'm not convinced he is electable anymore."

Mary Kai Nelson, 43, had been willing to forget about Hart's relationship with Rice, a Miami model. "I came in thinking maybe he has something to tell me," she said. She is one of 15 party regulars in this southeast Iowa Democratic stronghold invited by The Washington Post to watch the debate together. "I wanted to hear about all these new ideas he is supposed to have, but he didn't have any," she said forcefully. "He had nothing to tell me."

Most of the 15 Democrats in the group, which included several former Hart supporters, had expected the former Colorado senator to steal the show. But he left most of the group cold. Only Sen. Albert Gore Jr. (D-Tenn.), who was described by one in the group as "looking and sounding like a Republican," left a worse impression.

"Everyone thought he was the only competent candidate in the party that had any speaking ability or charisma," said Dennis Emanuel, an attorney. "The other candidates dispelled that. I think there are four or five candidates who most of us could support."

The surprise for the group of largely undecided Democrats was former Arizona governor Bruce Babbitt, the biggest dark horse in the race. The group's members said they were impressed by his humor, candor and willingness to take unpopular positions, as well as his refusal to send National Guard troops to training exercises in Central America when he was governor.

"To me, Babbitt was just another dark horse. I hadn't really paid any attention to him," said JoAnne R. Radosevich, 56. "He really came up in my estimation. I was very, very impressed with him. He came up with some good answers. He has some great ideas."

"This has been Babbitt's moment in the press for the last week or two," said Steve Welker, 38. "I wanted to see if the press was giving him a free ride or there was indeed some substance there. I came away very impressed. I really didn't have any feeling for him. Now, I'm going to go back and take a second look at him."

The debate, sponsored by the Des Moines Register, was considered the most important single event before the Feb. 8 Iowa precinct caucuses and was watched on public television by an estimated half of the approximately 100,000 Democrats expected to attend the caucues.

With Hart rejoining his rivals, expectations were high. But the two-hour debate lacked any grand moment or new arguments.

None of Hart's opponents attacked him on the "character issue" or asked him any tough questions. In effect, they diminished Hart by ignoring him. "He came. He saw. And he went," Babbitt said today.

The Hart camp felt the same frustration but blamed the content and format of the debate, rather than their candidate.

"It bores me to tears, the minutiae they get into," said Sue Casey, Hart's campaign manager. "If you're running for president, you don't want to be measured on whether plastic is biodegradable," she added, referring to an exchange between Massachusetts Gov. Michael S. Dukakis and Illinois Gov. James R. Thompson (R) Friday night on waste dumps.

But Hart, who seemed ill at ease and rusty, never found a way to transcend the format. "Instead of filling the void, he fell into it," said a manager for a rival candidate.

In the post-debate sessions at the Savery Hotel bar in Des Moines, where aides for the seven camps gathered with reporters until the wee hours of Saturday morning, a palpable sense of relief was felt that Hart had been cut down to size. And plenty of hopeful speculation was aired that now Hart has been stripped of his distinctiveness, the next thing to go will be his intensive media coverage -- the fuel, so far, of his low-budget campaign.

"When you get back in the race saying that you're the only one who has the answers, then unfortunately, you have to deliver," said Francis O'Brien, a spokesman for Dukakis.

The other candidate thought by most rival camps to have lost altitude was Sen. Paul Simon of Illinois, who was thrown off balance by Babbitt's question about why he accepts political action committee (PAC) contributions. Simon first hesitated, then denounced the corrosive impact of PACs, then said he will accept their money until the system is changed.

"This goes right to his strong suit -- integrity," said Michael McCurry, Babbitt's press secretary. "It's a real hot button issue among Iowa caucus goers, and we knew people out there would find it surprising that he takes PAC money."

Babbitt, Hart, Dukakis and Jesse L. Jackson refuse PAC contributions, while Simon, Gore and Rep. Richard A. Gephardt of Missouri accept them.

Simon, the front-runner in Iowa, said today that he didn't see "any significant breakthroughs" in the debate. "I don't think there were any stars. I don't think there were any losers."

Only Gore, who attacked the state's key role in the presidential nominating process, and Hart fared more poorly than Simon in the group assembled by The Post in Ottumwa, a heavily Democratic, blue-collar city of 27,000.

One-third of the group liked Simon more before the debate than after it. Former Wapello County Democratic Chairman Wayne Leach criticized Simon for "sounding like a typical politician with no substance." Sheila Davis-Welker, 31, was concerned "that he sounds real vague on how he's going to balance the budget." Two others in the group said they didn't like Simon's appearance, but several described him as "the most honest of all the candidates."

The group, which included some of the city's most prominent Democrats, was gathered to gauge the impressions of party regulars. It should not be regarded as a scientific sample.

Hart had several former supporters in the group, including Ottumwa Mayor Carl D. Radosevich. The mayor said he work "very hard" for Hart four years ago, but "lost faith" in him last spring, "not because of the morality thing, but because he didn't stand up and move with the thing."

"It was a crisis. Presidents have to manage many crises," Radosevich said. "A man who can't stand up when he has a failure is not going to stand up as president."

Several of the Democrats were leaning toward Dukakis at the beginning of the debate, but found his performance lackluster. He was described as being "the vaguest" candidate.

Gephardt and Jackson created a better impression. Nancy Emanuel liked Gephardt because "he is interested in the family farm. That's an issue that touches all of us in the Midwest." Raymond Young liked Gephardt because "he had all the toughest questions and handled them pretty well."

Young, a retired Teamster, praised Jackson. "He is saying a lot of things that the rest of the candidates ought to be saying," he said. "It's sad that a lot of people feel just because of his color they won't vote for him."