WASHINGTON — The Bush and Clinton families have towered over presidential politics for nearly 20 years. But in the West, another political family has loomed large for nearly a century.

Stewart Udall served as secretary of the Interior under presidents Kennedy and Johnson. His brother, Morris Udall, was a member of the U.S. House from Arizona for 30 years and ran against Jimmy Carter for the Democratic presidential nomination in 1976. Their cousin, Jesse A. Udall, served as an Arizona Supreme Court justice from 1960 to 1972, while several other family members have served in federal government and as federal judges.

Now, three great-grandchildren of prominent Mormon leader David King Udall are running for the U.S. Senate in 2008: Democratic congressmen Mark Udall of Colorado and Tom Udall of New Mexico, and Oregon Sen. Gordon Smith, a Republican.

Tom and Mark Udall are first cousins, while Smith is their second cousin. It would be the first time three members of one family served in the Senate at the same time.

Because he is related to the Udall dynasty through his mother, Jessica Udall Smith, and thus has a different last name, Oregon Sen. Gordon Smith is sometimes left out of discussions about the Udall family. But even though Smith is a Republican — unlike the better-known Udalls — Smith said he’s very much part of the family tradition.

“I’m as much Udall as they are, and I’m proud of both my paternal and maternal ancestry,” Smith said.

The political differences between Smith and the other Udalls goes back to ancestry too, he said. Great-grandfather David Udall had two wives in a polygamist marriage — a practice once common among Mormons, but no longer condoned by the church. The first wife was a Democrat and the mother of Stewart and Morris. The second, a Republican, was Smith’s great-grandmother.

“The Republicans have been a lot more prolific in having children,” Smith said. “The Democratic Udalls have been more prominent in national politics and made great contributions to our country.”

But a Udall family reunion in the upper chamber is far from a sure thing. Smith, with 11 years in the Senate, is a target of national Democrats. Mark Udall is neck and neck with his Republican opponent in Colorado, according to a recent poll. Only Tom Udall has a big lead early in his race, an open contest for the seat left by Sen. Pete Domenici.

While Smith did not know Tom and Mark well as children, he often saw their parents, Stewart and Morris, respectively, while growing up in the Washington, D.C., area. Now, the cousins meet for lunch every few months, Smith said.

“They’re my brothers and I love them, and we get together probably once a quarter and break bread over lunch,” Smith said. “They will often ask me Republican views on economics. I’m delighted to share them.”

Mark Udall said he and Smith are friendly despite party differences. Mark said he and Tom will likely campaign together next year, but he expects to stay out of the Oregon Senate race. Smith said he will also stay out of the Colorado and New Mexico races.

Another common conversation topic among the cousins is the environment — an issue closely associated with the legacies of Stewart and Morris. Morris, or “Mo” as he was known, is particularly remembered by environmentalists for pushing through a bill that set aside more than 150 million acres of land in Alaska as parks and wilderness.

Smith said he discussed environmental issues over dinner with Stewart Udall, now 87, sometime during his first term in the Senate.

“I told (Stewart) the irony was the environmentalists don’t like me because I’m trying to save the dams he built,” Smith said. “He had a good chuckle.”

Mark Udall, in turn, said he respects Smith for how he coped with the death of Smith’s son Garrett in 2003. Garrett Lee Smith committed suicide the day before he would have turned 22 after battling depression for several years, as Smith chronicled in his book “Remembering Garrett: One Family’s Battle With a Child’s Depression.”

Mark Udall said he’s also grateful that Smith has bucked his party and his church to back stem-cell research. Mark’s father, Mo, died from complications of Parkinson’s disease, which some scientists believe could eventually be treated with stem cells.

“His affection and respect for my father, which in a public policy way he made real by being an advocate for stem-cell research,” Mark Udall said. “That’s not orthodox in the Republican Party or even in the Mormon church.”

Just before Smith first entered politics in Oregon, he visited Mo Udall at Walter Reed Army Medical Center, to seek advice. Mo gave him a copy of “Too Funny To Be President,” one of several books Mo wrote about his political career.

“He said, ‘You use any of this material you like; I stole it all fair and square,’” Smith said.

When asked about Stewart’s and Morris Udall’s reputations for enjoying Washington’s nightlife, Smith chuckled.

“They were cultural Mormons, not practicing Mormons,” Smith said.

The Udalls have succeeded politically while belonging to a religion sometimes regarded with skepticism. Presidential candidate Mitt Romney, a Mormon, hoping to stop falling poll numbers, delivered a lengthy speech on religion recently, although he mentioned the Mormon church only once.

Tom Udall and Smith are both active members of the Mormon church, while Mark Udall calls himself “a descendant of Mormons,” and lists his religion as unaffiliated. Mark’s father, Mo, left the church after World War II, in objection to the Mormon church’s now-repealed doctrine forbidding blacks to serve as priests.

Early in his career, Smith said he worried that voters would reject him because of his religion. That proved not to be an issue in Oregon, where only 35 percent of the population was religiously affiliated in 2000, according to a study by the Association of Statisticians of American Religious Bodies. Mormons made up about 10 percent of the religious community, the study showed.

“I’m so proud of our state for so many reasons, but I think that one of the highest compliments that can be paid to Oregon is that one of its senators (Ron Wyden) is Jewish and one is Mormon, both from minority communities, and we work together as colleagues and friends in a bipartisan way,” Smith said.