DES MOINES, FEB. 2 -- With six days to go until the Iowa caucuses, the Democratic presidential campaign has taken on a sharper edge.

Former Arizona governor Bruce Babbitt, hoping to propel himself into the front ranks, has given four speeches -- each loaded with rhetorical bombs -- accusing three of his rivals of treating voters like "morons." At the same time, Rep. Richard A. Gephardt (D-Mo.), the leader in the polls here, has come under repeated attack.

Babbitt said Gephardt, Sen. Paul Simon (D-Ill.) and Massachusetts Gov. Michael S. Dukakis have all practiced the "politics of pander and appeasement" by their unwillingness to make hard choices to balance the budget while honoring the party's historic commitment to those most in need.

Dukakis, responding to Babbitt's attack, said, "It's unfortunate people feel they have to strike out in the closing days of a campaign. If you're going to lose, lose with dignity."

Babbitt also accused Gephardt of missing five votes to kill contra aid while he has been campaigning for president. "If he'd put his votes where his speeches have been, the contras would have lost," Babbitt charged.

Gephardt, who tonight flew to Washington to help lead the opposition to contra aid on the House floor Wednesday, responded outside a church: "He's just wrong, he doesn't understand the way Congress works. All of those votes were on continuing resolutions. Tomorrow is the showdown vote."

Gephardt predicted that the Democrats would defeat President Reagan's request for $36 million in military and humanitarian aid, and said the net effect of seven years of support for the contras has been "to drive the Sandinistas toward the arms of the Soviets."

In a foreign policy speech at the University of Iowa, Gephardt also said that as a result of Reagan's spending priorities, the United States is in danger of becoming "a muscle-bound giant . . . bristling with megatons, but without much of an economy to defend."

He pledged to observe what he called the "constitutional principle" that foreign policy is the result of a consensus between the president and the Congress, and noted he had been a lead sponsor of the so-called Boland Amendment that was breached when the Reagan administration secretly funneled profits from Iranian arms sales to the contras.

With Gephardt narrowly ahead in the polls on the strength of his anti-establishment appeals to farmers and workers, some of his opponents have begun nipping at his heels.

Jesse L. Jackson, who was in Kenosha, Wis., today to make a stand with 5,500 Chrysler Corp. workers likely to lose their jobs when a plant there closes, has called Gephardt a "Japan basher." Simon has been accusing him of "election-year conversions," citing what he said were inconsistencies on the MX missile, the B1 bomber, abortion and Social Security.

But these attacks have had a tame, almost reluctant quality to them. The Simon camp debated internally for weeks the merits of taking a more aggressive tack, finally concluding, in the words of one key adviser, that Simon would come off sounding like "just another politician if he went negative" -- thereby imperiling the essence of his appeal as an above-the-fray candidate of integrity, trust and comfort.

Babbitt has made the opposite tactical judgment. Running no better than fourth in any of the Iowa polls and badly in need of media attention, he has had something unpleasant to say about almost everyone. Among his comments:

"Dick Gephardt can be very persuasive," Babbitt said. "But the facsimile of convictions is no substitute for conviction itself. As he has climbed the ladder of the political establishment . . . , Dick has consistently discarded positions which grew inconvenient and consistently adopted new ones which seemed popular at the time . . . . When Congressman Gephardt, the lifelong political insider, becomes candidate Gephardt, the scourge of the establishment, he shows a versatility of conviction that takes your breath away."

Of Simon, Babbitt asks: "Does a real Democrat support a balanced-budget amendment -- even while proposing the most expensive public works project since the Egyptian pyramids, and so many new spending programs that his staff can't even count?"

He called Dukakis "an imaginative governor with an unimaginative campaign, an honest man with a campaign based on illusion. He has ducked and run from every tough issue. The greatest threat to our economic future is a crushing federal deficit, and Mike's answer is a fraud. For months, Mike led voters to believe he could raise $110 billion a year in new revenue -- just by hiring more tax collectors. That's not just a failure of policy, it's a failure of candor, a failure of courage and a political failure of the most serious kind."

Babbitt's attacks were largely ignored by his rivals, and his campaign manager, Fred DuVal, said the attack strategy was an acknowledged risk, based on the calculation that "we aren't going for 51 percent of the vote, we're going for 25 percent of the vote. We want to drive up the intensity factor, and this is the way to do it."

Staff writers David S. Broder and Lloyd Grove contributed to this report.