POLITICS : Races With GOP Incumbents Will Test Winds of Voter Anger : Delaware Senate contest is a case in point. If Democratic challenger wins, it may hint that ballot bashing is against long-termers more than party in power.

Striving to unseat this state’s long-entrenched senior senator in the November elections, an aggressive challenger is vowing to “send a wake-up call to Washington” and pledging not to seek more than two terms on Capitol Hill.

Much the same strategy is being used by Republican candidates around the country as they seek to capitalize on the public’s distaste for incumbents. The difference here in Delaware is that the challenger is a Democrat, state Atty. Gen. Charlie Oberly, and the incumbent is four-term Republican William V. Roth Jr.

The outcome of the campaigns in Delaware and two other states where Democrats have a reasonable chance to unseat incumbent Republican senators will help to illuminate the prospects for the 1996 election by testing the conflicting explanations of the national mood offered by the two political parties.

Are the Democrats right in contending that voters are generally sore at all members of Congress, most of whom just happen to be Democrats? Or are the Republicans correct in claiming that voter resentment is a specific reaction to Democratic control of both Congress and the White House?

An upset victory here would provide great comfort to Democrats nationally as they struggle to maintain their hold on the Senate. Needing a net gain of seven seats to oust the Democratic majority, Republicans are hoping not only to win seats left open by Democratic retirements but also to unseat Democratic incumbents, more than half a dozen of whom are in jeopardy.

By contrast, Democrats privately concede they have a plausible chance of turning out only three Republican incumbent senators--Roth, Conrad Burns in Montana and Slade Gorton in Washington. Some consider the Delaware lawmaker their best target simply because he has been around so long, ranking 10th among all senators in seniority and sixth in his own party.

Oberly has made Roth’s tenure the central theme of his campaign, arguing that the senator has lost touch with voters. It’s a tactic that has led Roth’s staff to cry foul.

“The attorney general is running a campaign based on age discrimination,” said Jo Anne Barnhart, Roth’s campaign manager. She specifically cites an Oberly television commercial that alters the speed of taped footage to show the 73-year-old Roth trudging along the campaign trail in slow motion. “It’s a real distortion.”

Oberly, 47, argues that Roth “has made age an issue by failing to show up for joint appearances” and complains that the senator refuses to debate him on television.

The two campaigns also squabble about the length of Roth’s lead. Oberly’s aides contend that their candidate, who started out 30 percentage points behind, now trails by only a single-digit margin. Aides to Roth insist that he still holds a comfortable advantage.

Delaware seems an unlikely place to exploit anti-incumbent fever. Roth’s Democratic colleague in the Senate, Joseph R. Biden Jr., is serving his fourth term. John Williams, the Republican whom Roth succeeded in 1970, served four full terms before retiring. No incumbent running statewide has been defeated in 10 years.

Analysts say Delaware incumbents have long careers because voters are practical enough to realize that as citizens of the state with the sixth-smallest population, their interests benefit from the extra prerogatives that come with Capitol Hill seniority.

“I don’t worry about people staying in office too long,” said Roth supporter Benjamin Perona, a retired businessman who showed up at the local Veterans of Foreign Wars post last week to watch Roth get that group’s endorsement. “They get to be chairmen of big committees and they stay there and hold power.”

As Roth likes to point out, he is the ranking Republican member of the Senate Committee on Governmental Affairs, a forum that allowed him some years back to expose such examples of government waste as the Navy’s $640 toilet seat. He also ranks third in seniority among Republicans on the Finance Committee, and in the late 1970s, he joined with then-Rep. Jack Kemp of New York in promoting sharp cuts in income tax rates. That idea became the foundation of President Ronald Reagan’s supply-side economic policies.

Roth sought to stress the benefits of his incumbency at a rare joint appearance with Oberly last week before members of Wilmington Women in Business, claiming that he is in a strong position to push for tax proposals to help small business as well as expansion of individual retirement accounts. Delaware, he claimed, needs his “power and experience to have a strong voice in Washington.”

By contrast, Oberly made a highly personal pitch, recalling how under his joint-custody arrangement with his ex-wife, he had taken over much of the burden of rearing their young children while she concentrated on finishing medical school.

“I can’t be your gender,” he told the women in attendance, “but I can understand your concerns.”

Oberly tries to make an asset of his divorce--a far cry from the days when the breakup of a marriage was considered near fatal for politicians. He stresses his friendship with his ex-wife, who has assumed much of the responsibility of parenting while he runs for office, and adds that her second husband is now his dentist.

Another reason, besides status and power, for the long tenure of Delaware officeholders is that their relative intimacy with the citizenry seems to breed affection rather than contempt. “We know our politicians very well,” said University of Delaware political scientist James Soler. “Charlie (Oberly) is Charlie and Bill (Roth) is Bill.”

“Delaware is a small state, and we go everywhere,” Roth said. “Frankly I have never had a warmer reaction than during this campaign.”

But even in this cozy enclave, discontent has reared its head. “Politicians aren’t really in there for the good of the country, they’re in there for the power,” Gloria Keiper, a secretary at Du Pont & Co., told a reporter after shaking hands with Oberly one noon hour last week. A Roth voter in 1988, she said she has decided to vote for Oberly next month because “if somebody has been there too long, better get him out.”

Giving added bite to the issue of anti-incumbency in this normally placid state, analysts say, is concern over Roth’s age that stems, in part, from arguments Roth himself has made. Soon after he entered the Senate, he proposed a constitutional amendment banning senators from running after they turn 70, a favorite idea of Williams, his predecessor and mentor.

Oberly’s campaign has reminded the voters of this in a television commercial accusing Roth of bending his principles to serve his political ambition.

Roth attributes the amendment to “the folly of my youth” and argues that any such dictum would now be considered age discrimination.

Oberly’s chances for success depend far more on his argument that the state needs fresher leadership than on significant issue differences with Roth. “Economically, there is not a whole lot of difference between us,” Oberly, who prides himself on his fiscal restraint, said in an interview.

Although he claims to be more interested than Roth in supporting social programs such as Head Start and day care, Oberly says he does not know how he would raise the money to expand such efforts. “The deficit is strangling us. But we can’t raise taxes on middle-class Americans.”

Here are Democratic prospects in the two other states where they have the most hope of overturning GOP incumbents:

* Montana: Democrat Jack Mudd, an attorney and champion of the environmental movement, has been trying to depict Burns as a tool of special interests because of the one-term Republican’s trips to such events as the Orange Bowl and the Kentucky Derby as the guest of lobbyists.

Burns contends that his travels have been intended to boost the Montana economy by promoting tourism and trade, and he points to his better than 99% voting attendance record in the Senate. A poll taken late last month for Montana’s Lee newspapers showed Burns with a 15% lead.

* Washington. Democrats have long viewed Republican incumbent Gorton as a likely target. He won election in 1988 by only two percentage points in a state that President Clinton carried handily in 1992. Democrats believe his cerebral style has not endeared him to the Washington electorate.

Still, in the Sept. 20 primary involving candidates from both parties, Gorton got a bigger share of the vote than all four Democratic candidates combined, including Ron Sims, who emerged as the party’s nominee.

Some analysts say that Sims, a member of the King County (Seattle) Council and the first black Senate nominee in the state’s history, may be hurt by his liberal image. A poll taken for the Spokane Spokesman-Review newspaper and two television stations in mid-October showed Gorton with a 20-point lead, with 16% of voters undecided.