MANCHESTER, N.H., FEB. 11 -- Sen. Paul Simon (D-Ill.) pulled out the New Hampshire primary campaign's version of long knives today, sharpening his attack on Rep. Richard A. Gephardt (D-Mo.) with a new round of radio and television advertising.

The New Hampshire front-runner, Massachusetts Gov. Michael S. Dukakis, meanwhile, remained largely aloof from the growing debate over Gephardt's record. Campaigning almost regally on the eastern edge of the state while his closest primary opponents slugged it out with each other in the west, Dukakis said that in spite of polls showing him with a comfortable lead over both Simon and Iowa winner Gephardt, he is running his campaign "like we're 10 points behind."

"We've all got to defend our records," Dukakis said when asked about the Gephardt-Simon challenges.

Simon's cash-strapped campaign deferred staff paychecks and borrowed $110,000 from a Washington bank Wednesday to pay for the new advertising, taking a gamble that his campaign, which admits to being $500,000 in debt, will overtake Gephardt for second place in Tuesday's primary.

The television ad shows a picture of Simon and one of Gephardt as an announcer asks: "Who can we trust?" The tougher radio version opens: "Sometimes a candidate's toughest opponent can be his own record," and goes on to chronicle Gephardt votes in favor of such conservative causes as the MX missile, B1 bomber, neutron bombs and chemical weapons. Simon said he opposed such legislation.

Simon adviser Paul Maslin said that the new approach was necessary because "you have a very brilliant campaign being run that is in direct contradiction with his record."

If airing Gephardt's record can be considered negative, Simon said, "that says something about his record."

Gephardt responded that the new Simon campaign tactics "disappointed" him. "This is not the Paul Simon I know," Gephardt said at an appearance in West Canaan. "I like him. I respect him deeply, but he is taking bad advice from his consultants."

Gephardt also accused Simon of making his own flip-flop in voting for a Senate bill that would have frozen Social Security benefits.

Gephardt campaign manager William Carrick called Simon's new ads "just a fleabite."

Dukakis, meanwhile, basked in the approval of activists who have fought the multibillion-dollar Seabrook nuclear plant located along the state's resort seacoast.

"Seabrook really is only a symbol of what's wrong with our energy policy," said Dukakis, who as governor of Massachusetts has held up the licensing for Seabrook by refusing to approve evacuation plans.

Dukakis, whose once commanding lead in the polls has fallen sharply since his third-place finish in Iowa, told a Portsmouth audience that the last time he trusted polls was in 1978, when he ran for governor and lost. "The Red Sox that year were 14 games ahead at the All-Star break," he said. "And we all know what happened to both of us."

No candidate campaigning in New Hampshire has been able to escape the nuclear power issue. Yesterday, Simon used the Seabrook plant as a platform from which to launch another Gephardt attack. And on Friday, Gephardt is scheduled to make his own Seabrook pilgrimage.

But to the extent that an anti-Seabrook stance is a popular one in the Granite State, Dukakis is in the best position to reap its benefits.

"More than 60 percent of the people in New Hampshire are opposed to opening Seabrook, even if it costs them money," said Paul McEachern, a Dukakis supporter who is running for governor against incumbent John Sununu.

Sununu, who is Vice President Bush's New Hampshire campaign chairman, favors opening the Seabrook plant.

Trailing Dukakis from one stop to another today was David Scanzoni, a spokesman for New Hampshire Yankee, the management company that operates Seabrook. Dukakis, he told reporters, has turned the future of Seabrook into "a political issue for his gain and hurt the regional economy."

Scanzoni said New England will face an electricity shortage within the next few weeks if Seabrook, which was completed in 1986 but remains unopened, is not allowed to go on line.

Public Service of New Hampshire, which owns 35 percent of Seabrook, declared bankruptcy last month, blaming its financial straits in large part on the delay in opening the plant. Staff writer Paul Taylor contributed to this report.