BOSTON -- At age 46, running for relection as the junior U.S. senator from Massachusetts, Democrat John F. Kerry is a tested, savvy politician. His Republican opponent, James Rappaport, is a 34-year-old political rookie best known for being the son of a wealthy Boston real estate developer.

Why is Kerry in a close race?

"You just explained why," said pollster Brad Bannon. "The fact he {Rappaport} has never run for anything explains his popularity."

Such is the depth of public anger at incumbents here in Massachusetts. In the Sept. 18 primary, voters rejected every real and perceived incumbent on the statewide ballot, from the current and former attorneys general to the current and former House speakers.

The trend has spooked the Democrats. Because they hold every state and federal elective office in Massachusetts (except for one House seat), the Democrats have much to lose when voters decide to turn politicians out of office.

In the Rappaport camp, the "I'm-not-Kerry strategy" is simple. The candidate's advisers have spent lavishly from the Republican candidate's personal fortune to depict Kerry as a classic "tax-and-spend liberal." They also hammer away at Kerry's links to the intensely unpopular Gov. Michael S. Dukakis, noting that Kerry was Dukakis's lieutenant governor and later his "ambassador to Washington."

In one particularly dramatic television ad, known as "Metamorphosis," the Rappaport team presents voters with an unflattering black-and-white portrait of Dukakis that evolves into a picture of Kerry's face.

Politicians and their advisers report unprecedented levels of voter anger in Massachusetts, driven by the continuing fury at Dukakis and his Democratic allies for losing the presidency and wrecking the state's balance sheet. The anger is fueled by the regional economic recession and, more recently, by the failure of Congress and President Bush to deal with the federal deficit.

"I think here in Massachusetts, it is still building and is exacerbated by what voters see happening in Washington. That has brought Kerry into the danger zone," said Bannon, who is not aligned with either camp. "If it does turn out to be a referendum on incumbency, Kerry might as well pack it in rght now."

That would suit Rappaport, who has been attacking Kerry for most of 1990. Although Rappaport lost his party's endorsement to an antiabortion businessman, Dan Daly, Rappaport put about $1.7 million of his money into the Sept. 18 primary and won it. Much of the money went for advertising designed to convince voters that Rappaport was already running against Kerry.

Kerry, who had no primary challenger, did little during the spring and summer to counter Rappaport's ad campaign. Only since the primary has Kerry begun to fight back, and both sides have subjected voters to nonstop negative campaigning.

Both sides have tried to exploit the savings and loan crisis. Rappaport aides have tried to interest reporters in stories about Kerry's purported ties to David Paul, deposed chairman of Florida's CenTrust, who was a major donor to Democrats in 1987-88, when Kerry headed the Democratic Senatorial Campaign Committee.

Kerry, for his part, charges Rappaport with "profiteering" from the S&L meltdown by turning a 4,000 percent profit in 18 months on a Hawaiian condominium complex that a Rappaport partnership bought in 1987 from a distressed federal thrift agency.

In print, on the air and in person, the candidates have slogged through other personal matters:

Rappaport pounced on Kerry's suggestion that Bush leave some "wiggle room" for Iraq to withdraw from Kuwait, saying Kerry wanted to make "concessions to Saddam Hussein." Kerry, a decorated Vietnam veteran, denied going soft on Iraq, and veterans angrily rallied round him.

Rappaport hit Kerry for voting against the death penalty for major drug traffickers and faulted the Democrat, who serves on the Foreign Relations Committee, for "being more interested in Central America than in central Massachusetts."

Kerry, who has released his tax forms, demanded Rappaport follow suit and played up the rich-kid theme, saying, "His only qualification for the job, it seems, is a seven-figure bank account." Rappaport says he will make all disclosures required by law.

Kerry charged Rappaport with hypocrisy for criticizing "federal subsidies" when Rappaport's family fortune came largely from the federally subsidized Charles River Park development in Boston's West End and when Rappaport got farm subsidies while running his family's Vermont dairy operation.

At this rate, many voters may never find out that Rappaport is a lawyer-businessman, married with two children. Or that he is a fiscal conservative who wants to lower taxes, balance the federal budget and give the president a line-item veto. Or that he is a moderate on many social issues, favoring the status quo on abortion and tax credits for child care.

As Kerry and Rappaport fire away, that may not matter.