Republican presidential candidate Jack Kemp is to unveil new television commercials in Iowa and New Hampshire tonight attacking his party's two front-runners as champions of higher oil prices and reduced Social Security benefits.

Rep. Kemp's new ads raise the perennial question of whether negative advertising is a legitimate or effective tool against a campaign opponent.

A spokesman for Vice President Bush's campaign yesterday called one of the commercials "a blatant lie," while a spokesman for Senate Minority Leader Robert J. Dole (R-Kan.) warned, "When you put on a mean message, many people are turned off."

The New York congressman is so far the only candidate of either party to make wide use of such commercials, which Kemp press secretary John Buckley calls "issue-oriented comparison spots." Buckley attributed a recent 5-point jump in Kemp's New Hampshire poll standings largely to a television blitz attacking Bush and Dole as tax-hikers.

The latest 30-second Kemp commercial, to be aired in frigid New Hampshire, where heating costs are an emotional issue, charges that Bush and Dole are "Washington insiders {who} want higher oil prices."

A tuxedoed Bush is shown smiling with Saudi King Fahd, while Dole is shown standing behind a lectern, as the announcer says: "George Bush told the Arabs to keep oil prices up, and Bob Dole supports a tax increase on imported oil."

Kemp's 30-second Iowa spot claims that Bush and Dole voted in the Senate to "cut future Social Security benefits," and that Kemp "rush{ed} to the White House to persuade President Reagan to stop this plan to cut Social Security."

Kemp opposed a one-year freeze in Social Security cost-of-living increases, which was proposed by President Reagan and narrowly passed by the Senate as part of the federal budget package in May 1985. Reagan eventually bowed to pressure and dropped his support for the freeze.

Peter Teeley, Bush's campaign press secretary, denounced the commercials as an example of "public officials consciously distorting the records of other candidates."

"The accusations regarding the vice president and higher oil prices are blatant lies," Teeley said. "Basically what this is," he added, "is an effort by a campaign that's going down the tubes to resurrect itself."

Buckley said the oil-price charge refers to remarks Bush made before a tour of Arab oil-producing nations in April 1986 -- comments widely interpreted at the time as a serious political gaffe. It is "essential," Bush said then, "that we talk about stability {of oil prices} and that we not just have a continued free-fall, like a parachutist jumping out without a parachute."

Dole spokeswoman Katie Boyle, meanwhile, denied that the senator supports higher oil prices. "Dole says he would consider an oil import fee if it was needed to stabilize prices, not to reduce the deficit, and if a rebate provision would be included" for home heating oil consumers. As for Social Security, she said Dole supported "freezing a cost-of-living increase, but that's not 'cutting.' "