Sen. Rudy Boschwitz (R-Minn.) was the only Senate incumbent in danger of defeat early today as nearly all other senators coasted to victory and Democratic Sen. Bill Bradley in New Jersey narrowly survived a surprisingly strong challenge from Christine Todd Whitman, a relatively unknown and underfinanced Republican.

Based on conclusive returns from yesterday's voting in all states but Minnesota, the Senate appeared likely to see little if any change in the Democrats' 55 to 45 majority over Republicans. Boschwitz's defeat would increase the Democratic advantage to 56 to 44.

Not since 1856 have all Senate incumbents won, according to the Library of Congress. If only one is defeated, it would be the first time since 1962 that incumbents did so well. The strong showing of the Senate incumbents came despite widespread dissatisfaction with Congress and the conduct of campaigns.

In the high-profile, hotly contested race that was expected to produce a record turnout in North Carolina for an off-year election, Sen. Jesse Helms (R-N.C.) defeated Democrat Harvey Gantt, the black former mayor of Charlotte, by about 8 percentage points.

In two late breaking races, Sen. Daniel K. Akaka (D-Hawaii) defeated Rep. Patricia F. Saiki (R), who was expected by her party to win; Boschwitz was narrowly trailing challenger Paul Wellstone (D).

In the New Jersey race, which neither party had regarded as close before votes started pouring in for Whitman, Bradley was locked through most of the evening in a struggle with the former state public utilities commissioner, who had made a big issue out of recent state tax increases.

With nearly all the votes counted, Bradley, who is regarded as a leading Democratic presidential prospect in 1992 or later, led Whitman by 52 to 48 percent.

Bradley outspent Whitman by more than 20 to 1, according to final preelection spending reports. But he was apparently hit hard by a voter backlash against Democratic Gov. Jim Florio's $2.8 billion tax increase, which Bradley refused to address in his campaign.

In Kentucky, where the Senate race appeared to tighten toward the end of the campaign, Sen. Mitch McConnell (R) won, defeating Harvey Sloane (D), a former mayor of Louisville.

In Minnesota, the lead see-sawed through the night between Boschwitz and Wellstone, a little-known maverick who was boosted by turmoil in the state GOP. With 55 percent of the vote counted, Wellstone led by 2 percentage points.

In Massachusetts, Sen. John F. Kerry (D) defeated Jim Rappaport (R) despite an early scare for Kerry in a voter backlash against Democratic officeholders.

In Iowa, Sen. Tom Harkin became the first Democrat ever reelected to the Senate, defeating challenger Rep. Thomas J. Tauke (R) after a hard-fought and seemingly close race.

In two other races that had once been regarded as potentially close, Sens. Paul Simon (D-Ill.) and Carl Levin (D-Mich.) won easy victories over their House GOP challengers, Reps. Lynn Martin (Ill.) and Bill Schuette (Mich.).

In another race that Republicans had targeted for an upset, Senate Foreign Relations Committee Chairman Claiborne Pell (D-R.I.), handily overcame a challenge by Rep. Claudine Schneider (R).

Another veteran, Sen. Mark O. Hatfield (R) of Oregon, defeated Harry Lonsdale (D), who had closed in on Hatfield in the last few weeks of the campaign with a strong anti-incumbent pitch.

Republicans won all three races for open seats being vacated by retiring Republicans. Rep. Robert C. Smith (R) easily won victory over former senator John Durkin (D) in New Hampshire. In Colorado, Rep. Hank Brown (R) defeated Josie Heath (D). In Idaho, Rep. Larry E. Craig (R) trounced Ron Twilegar (D).

Early returns from Alaska showed Sen. Ted Stevens (R), heavily favored to win reelection, with a strong lead.

Elsewhere, Sens. Albert Gore (D-Tenn.), Max Baucus (D-Mont.), Joseph R. Biden Jr. (D-Del.), John D. "Jay" Rockefeller IV (D-W.Va.), Howell Heflin (D-Ala.), Phil Gramm (R-Tex.), David L. Boren (D-Okla.), Dan Coats (R-Ind.), William S. Cohen (R-Maine), J. James Exon Jr. (D-Neb.), Nancy Landon Kassebaum (R-Kan.), Larry Pressler (R-S.D.), Pete V. Domenici (R-N.M.), Alan K. Simpson (R-Wyo.) and Strom Thurmond (R-S.C.) coasted to easy victories.

Four senators -- Thad Cochran (R-Miss.), Sam Nunn (D-Ga.), David Pryor (D-Ark.) and John W. Warner (R-Va.) -- won reelection by default when no major party opponents filed to oppose them.

In Hawaii contest, Akaka led Saiki by 9 percentage points with almost three-quarters of the ballots counted.

Even before the polls opened yesterday, chances appeared remote that there would be much change in the Democrats' 10-vote margin in the Senate despite heated races in many states.

Republicans conceded there was no chance they could oust the Democrats from the majority they have held since 1986. And Democrats harbored few illusions that they could gain enough seats to muster the 60 votes needed to stop GOP filibusters or the 67 votes necessary to override a presidential veto.

But even a small change in the Senate's makeup could strengthen President Bush's hand in dealing with the Democratic-controlled 102nd Congress that will convene Jan. 3, or, conversely, embolden the Democratic leadership in challenging administration positions.

Already reelected was Sen. J. Bennett Johnston (D-La.), who fended off a surprisingly strong challenge from former Ku Klux Klan leader David Duke in the state's open primary a month ago. Under Louisiana law, candidates can avoid a runoff in November if they win a majority of all primary votes, as Johnston did. Duke, running as a Republican to the dismay of many national party leaders, took 44 percent of the vote.

Of the 34 seats at stake yesterday, 16 were held by Democrats, all of whom sought reelection. Akaka, a House member appointed six months ago to succeed the late Sen. Spark Matsunaga (D) was regarded as the Democrats' most vulnerable incumbent.

The other 18 Senate seats were held by Republicans, 15 of whom sought reelection. The three Republican retirees, William L. Armstrong (Colo.), James A. McClure (Idaho) and Gordon J. Humphrey (N.H.), are from the conservative wing of the party, as were the GOP candidates to succeed them.

From the start, this year's elections were viewed as a warmup for an all-out battle for control of the Senate in 1992, when Democrats will be defending 20 seats, the Republicans, 14. Many of the seats that the Democrats will be defending then were picked up in 1986, when the party regained control of the Senate, ending six years of Republican majority.

Republicans figured that if they could pick up two or three seats this year, they would be within striking distance of recapturing control of the Senate in 1992, when they are counting on a boost from an expected reelection bid by Bush. Democrats said they would be content to hold their own at 55 seats this year.

Even though the party that wins the White House usually loses congressional seats in the next off-year election, Republicans began this year with high hopes, having recruited numerous veteran House members -- seven incumbents and one former member -- to challenge vulnerable Senate Democrats. By contrast, the highest-ranking challengers recruited by the Democrats were state legislators.

But, as the year wore on, an anti-Washington, anti-incumbent mood swept the country, exacerbated toward the end by a tumultuous budget fight between Congress and the White House. The Republican House members who were challenging for Senate seats were themselves seen as Washington insiders, and thus lost the edge they were seeking.

Even more important was the growing financial advantage enjoyed by incumbents of both parties.

Only eight major party candidates who challenged incumbents in the general election were able to raise at least half as much as the incumbents did, according to an analysis by the self-described citizen's lobbying group Common Cause, based on final preelection financial reports submitted Oct. 17.

Incumbents outraised challengers by more than 3 to 1, winding up with seven times as much cash for the final three weeks of the campaign, according to the Common Cause analysis. Political action committees (PACs), usually representing special-interest groups, gave four times as much to incumbents as they did to challengers.

As in 1984 when Helms last campaigned, the most expensive race of the year was in North Carolina, where expenditures as of Oct. 17 totaled $19.3 million, including $14.8 million for Helms and $4.5 million for Gantt. The Illinois Senate race ranked second at $12 million. In Texas and New Jersey, ranked third and fourth respectively, incumbents outspent their challengers by 10 to 1 or more.