ATLANTA, FEB. 27 -- Massachusetts Gov. Michael S. Dukakis heaped scorn on the credentials and accomplishments of rivals Rep. Richard A. Gephardt (Mo.) and Sen. Albert Gore Jr. (Tenn.) in a nationally televised Democratic presidential debate this afternoon aimed at voters in the 20 states casting ballots on March 8.

Showing an aggressive, almost prosecutorial style of ridicule not seen in previous encounters, Dukakis ripped Gephardt's tax and trade record and scoffed at Gore's diplomatic skills.

The two rivals returned the fire, but their barbs did not have nearly the sting of Dukakis'.

In rapid succession, Dukakis:Needled Gephardt repeatedly for his 1981 vote for the Reagan tax-cut bill, asking reproachfully, "Are you proud of that vote?" When Gephardt responded that he was "proud to cut taxes on ordinary, middle-income working families," Dukakis interjected like a lawyer before a jury: "Let the record show that Congressman Gephardt apologized all over Iowa for that vote before he came down south." Said Gore was taken "to the cleaners" by the Reagan administration "the only time he ever conducted a negotiation." He referred to Gore's role in a 1983 compromise that kept alive the MX-missile program and resulted in a new bargaining approach to the Soviet Union. Declared the Gephardt amendment to the trade bill "dead," adding, "its burial has been postponed until after 'Super Tuesday' in deference to the next of kin." He referred to a decision by House-Senate conferees to postpone a vote on the provision, which is the centerpiece of Gephardt's campaign, until after the March 8 voting.

Jesse L. Jackson, the other candidate battling Dukakis in the South, warned Dukakis that "taking potshots" could "devolve to the level of the Republican debacle" and make unity more difficult at the Democratic convention here in July. The other two candidates on stage for the debate sponsored by the Atlanta Journal and Constitution, Sen. Paul Simon (Ill.) and former senator Gary Hart (Colo.), were as marginal in the debate as in the Super Tuesday contests, but managed to make the point that they consider themselves potential brokers at the convention.

Hart acknowledged that "the chance of my being the nominee is very remote" but said "people who support my views have a right to be represented" in event of a deadlock.

Dukakis' aggressive tactics appeared to be a preemptive strike against the two candidates, other than Jackson, with closer affinity to the 14 southern and border states voting on Super Tuesday. Despite his "outsider" label, the governor has the most extensive organizations in the region. His strategists believe he can get a plurality of the delegates in the South unless Gore and Gephardt succeed in the next nine days in painting him as an unacceptable choice for southerners.

Dukakis went out to nail them before either challenged him. Citing a target he has used before, Dukakis said, "The 1981 tax bill was a disgrace, and Dick {Gephardt} voted for it . . . ."

When Gephardt defended his vote, saying that two-thirds of the reductions went to people earning less than $50,000, Dukakis said the bill "resulted in massive deficits . . . created most of the trade problems you've been talking about and opened up loopholes for the wealthy. Even {former budget director} David Stockman said it was pigs feeding at the trough."

Gephardt responded, "Your kind of stance on taxes in Massachusetts is one that raises taxes on ordinary, average middle-income families."

"I've cut taxes five times in the last four years," Dukakis protested.

"But you raised taxes about 10 times," Gephardt shot back.

"You know I haven't raised taxes," Dukakis said, never yielding the floor. "All I want to know is are you proud of that vote?"

When moderator John Mashek, the newspapers' senior political correspondent, asked about the need for new alliances, Dukakis went after Gore, the rival who had most persistently questioned the governor's foreign policy credentials.

"Al Gore has never run a government, never balanced a budget, never had to shape an administration, never had to work with a legislature. The only time he ever conducted a negotiation was the MX negotiation and the administration took him to the cleaners. One of his colleagues said, 'I shudder to think what would happen if he negotiated with the Soviet Union.' "

Gore did not respond immediately, but at the first opportunity, he defended his "long and deep experience" in foreign affairs and said, "We have seen the consequences in the last seven years of having a president who needs on-the-job training." Citing Dukakis' statements implying that he would accept a client state in Central America and consider removing U.S. troops from South Korea, Gore said, "You are the one who raises the questions of your lack of foreign policy experience."

Later, in the press room, Gore added that Dukakis' performance illustrated "the danger of trying to learn foreign policy in a two-day cram course at the Kennedy School {of Government at Harvard University}."

The Gephardt camp expressed surprise at Dukakis' combativeness. "It's a thin line between being shrill and impolite and exuding strength," said William Carrick, Gephardt's campaign manager. "I thought he was over the line."

While Gephardt never found a moment to tell those watching the CNN telecast of his support from three dozen southern House colleagues, Gore managed to associate himself repeatedly with the policy views of Sen. Sam Nunn (D-Ga.) and former president Jimmy Carter.

But it was Jackson, at the end of the 90-minute debate, who made the most adroit regional appeal. "I sit here today as a proud son of the South," said the Greenville, S.C., native. "The only one who received his high school diploma from the South and his college diploma from the South."

Gore, who has been reminded frequently that he graduated from St. Alban's, a private school in Washington, D.C., did the best he could to parry. "My high school diploma," he said, "is from the same school where Jesse Jackson sends his son."

Staff writers James R. Dickenson and Tom Sherwood contributed to this report.