WASHINGTON — Four Senate candidates are about to test anew whether, when it comes to American politics, the son also rises.

Republican Thomas Kean Jr. in New Jersey and Democrats Bob Casey Jr. in Pennsylvania and Harold Ford Jr. in Tennessee — all making their first Senate bids — are in tight races. Senator Chafee, a Republican, is fighting for survival as he seeks a second term in Rhode Island.

In a country where George W. Bush is president and Hillary Clinton is the leading Democratic contender for the White House in 2008, it isn’t surprising that family ties help. “The importance of family in politics is as American as apple pie,” a history professor at Boston University, Julian Zelizer, who has written books about Congress, said.

Six current senators are the offspring of former senators: Democrats Chris Dodd of Connecticut, Evan Bayh of Indiana, and Mark Pryor of Arkansas; and Republicans Chafee, Robert Bennett of Utah, and Lisa Murkowski of Alaska.

Numerous others in Congress are carrying on a family tradition — by marriage as well as by blood — including Mrs. Clinton, a senator from New York, and Senator Dole of North Carolina. Ms. Clinton’s husband, President Clinton, defeated Ms. Dole’s, a former Senate majority leader Bob Dole, in the 1996 presidential election.

Other heirs to political legacies who are running this year include Jack Carter, son of former President Carter and the Democratic nominee for the Senate in Nevada; Democrat Chet Culver, son of a former senator, who’s running for governor in Iowa; and Beau Biden, son of Democratic Senator Biden, seeking to become Delaware’s next attorney general. Democrat John Sarbanes, running for a House seat from Maryland, is the oldest son of retiring Senator Sarbanes.

The races involving Messrs. Casey, Kean, Ford and Chafee are among the ones political observers are watching closely as they assess Democrats’ chances of picking up the six seats needed to gain control of the Senate.

Mr. Casey, campaigning to unseat Republican Senator Santorum in Pennsylvania, is discovering that a political legacy can be double-edged. While Mr. Casey got his start in politics with help from his father, former Governor Robert Casey, Mr. Santorum tried to throw Mr. Casey’s family connections in his face during a debate.

Mr. Santorum, 48, seeking a third term, needled Mr. Casey by saying his father “would be very upset if he were alive today” by his son’s support for the so-called morning-after pill favored by abortion-rights advocates to prevent pregnancies.

Democrats picked state Treasurer Mr. Casey, 46, in part because of his appeal to anti-abortion Democrats who have supported Mr. Santorum in his two previous Senate runs.

Political ancestry is most valuable for a challenger because it confers name recognition. “You don’t have to work nearly as hard to get your name known to the voters,” said Wendy Schiller, a political scientist at Brown University in Providence, Rhode Island.

By this reasoning, Mr. Kean, 38, who traces his lineage back to a delegate to the Continental Congress, should be the biggest beneficiary. A New Jersey state senator, he is the son of former Republican Governor Tom Kean Sr.

“It’s the biggest name in Jersey state politics,”said David Rebovich, a political scientist at Rider University in Lawrenceville, New Jersey.

The elder Mr. Kean, who was also cochairman of the bipartisan commission that investigated the September 11, 2001, terrorist attacks, joined his son on the campaign trail last week at Kean University in Union. The institution, founded in 1855, moved to its current campus on Kean family property in 1958.

“Let me say this, and seriously, I support this candidate,”Tom Kean Sr. said to laughter from the audience. “It’s not just the family relationship. In Tom Kean Jr. we have the kind of young man that I have been trying to encourage for a long, long time to run for office.”

The younger Mr. Kean is trying to unseat Democratic Senator Menendez, 52, appointed by Governor Corzine earlier this year to fill the Senate seat Corzine resigned to become governor. Mr. Menendez is considered by political strategists to be the nation’s most vulnerable incumbent Democratic senator.

Mr. Ford, currently a congressman from Memphis, is seeking the Senate seat being vacated by Majority Leader Bill Frist. Mr. Ford was just 26 when he was first elected to the House in 1996, following the retirement of his father, Harold Ford Sr., who had held the seat since 1975.

The Ford family name comes with a burden. The day after Mr. Ford announced his Senate candidacy, his uncle, state Senator John Ford, was accused of taking $55,000 in bribes from a phony company set up by an FBI sting dubbed “Operation Tennessee Waltz.”

The congressman’s father successfully fought fraud charges stemming from a loan that he received from banks controlled by Jake Butcher and his brother, who went to prison following the collapse of their financial empire.

Mr. Ford, 36, who would be the first black senator from the South since 1881, has said he should rise or fall on his own record. He is running against former Chattanooga Mayor Bob Corker, 53.

The political legacy that helped Mr. Chafee, 56, get his job may not be enough this year. He is trailing Democrat Sheldon Whitehouse, 51, polls show.

The Republican Mr. Chafee is trying to win a second term in an overwhelmingly Democratic state by highlighting his opposition to some of Mr. Bush’s policies, notably the Iraq war. Mr. Chafee was appointed to the Senate in 1999 upon the death of his father, fourterm Senator John Chafee.

The Chafee name presents a challenge for Whitehouse because John Chafee “was someone who over a very long period of time earned the respect of people” in both parties, said Bill Lynch, chairman of the Rhode Island Democratic Party. Still, Mr. Lynch said, voters “‘see a tremendous difference” between father and son because the Republican Party has changed since the elder Mr. Chafee’s day. “We now have a situation where that seat is very much in play,” he said.

A famous father only gets a candidate so far, said Boston University’s Mr. Zelizer. “All sorts of issues can trump name recognition,” he said.