State Rep. Russ Carnahan (D), the son of the late Missouri Gov. Mel Carnahan (D) and former Sen. Jean Carnahan (D-Mo.), is likely to run for the open seat of retiring Rep. Richard Gephardt (D).

“I am very seriously proceeding with the race and expect to make a formal announcement soon,” Carnahan said in an interview Wednesday.

A Carnahan candidacy would create massive waves in the so-far-still pool of the 3rd district, where two Democrats — state Sen. Steve Stoll and St. Louis Circuit Clerk Mariano Favazza — are already running.

It would also set up a potential primary clash between Gephardt’s political machine, which Stoll claims is behind him, and the Carnahans, who have dominated Democratic politics in the Show Me State for decades. Favazza is not seen as a major factor in the race.

One Democratic source familiar with the process said the Gephardt people have not chosen a candidate either publicly or privately in the Democratic-leaning district, which takes in parts of St. Louis City as well as portions of St. Louis, Jefferson and St. Genevieve counties.

Russ Carnahan, 42, has a long political lineage: In addition to his parents, he is the grandson of former Congressman and Ambassador A.S.J. Carnahan. His sister, Robin, is pondering a run for Missouri secretary of state in 2004, according to a Democratic source.

Their father, Mel, held a variety of jobs in state politics, beginning as a municipal judge from Rolla in 1960 and rising to serve two terms as governor from 1992 to 2000.

He then embarked on a campaign against then-Sen. John Ashcroft (R-Mo.) that ended tragically when Carnahan, along with his eldest son, Randy, and a top aide, was killed in a plane crash on Oct. 16, 2000.

The election quickly turned into a tribute to Carnahan, and he posthumously bested Ashcroft 51 percent to 48 percent.

In December 2000, Jean Carnahan was appointed by acting Gov. Roger Wilson (D) to fill the vacancy. She ran in 2002 for the remaining four years of her husband’s term but was defeated by former Rep. Jim Talent (R), 50 percent to 49 percent.

A.S.J. Carnahan, Mel’s father, represented Missouri in the House from 1944 to 1958 and also served as ambassador to Sierra Leone under President John F. Kennedy.

Russ Carnahan believes the political legacy and know-how gained from his elders will serve him well in this Congressional race.

“My family has always been very close-knit and very involved in all of the campaigns we have undertaken,” he said. “My mother has given me some great advice and counsel and she will be a tremendous asset.”

Even Carnahan’s potential opponents acknowledge the power his last name conveys.

“The Carnahan name carries a lot in Missouri,” a Stoll aide said.

One Missouri Democratic operative noted, however, that Carnahan “doesn’t really carry much beyond the name.”

Saul Shorr, a media consultant who handled television ads for the Senate campaigns of both Mel and Jean Carnahan, said that “every time someone who has a name that is prominent runs, they have to prove that they are worthy on their own.”

But, he added: “In Russ’ case he will have no problem whatsoever backing [the name] up.”

Russ Carnahan is quick to note that he has cut a political path of his own.

First elected to the state House from a St. Louis City-based district in 2000, Carnahan currently serves as chairman of the Democratic Caucus. His district is entirely contained within the boundaries of the 3rd Congressional district.

Last cycle, Carnahan oversaw the campaign arm of his Caucus, and “helped out a lot of candidates around the state and in this district.”

This will be Carnahan’s second Congressional run. In a neighboring district, he challenged then-Rep. Bill Emerson (R) in 1990, taking 43 percent of the vote while being outspent by nearly $500,000. His father was lieutenant governor at the time.

Carnahan said he has been considering a run since the night he heard that Gephardt would not seek re-election and would instead pursue only the Democratic presidential nomination.

“From that evening I have been working with party officials and community leaders here and laying the groundwork to do this,” Carnahan said.

Carnahan’s likely candidacy puts him directly in the path of Stoll, who is considered the race’s frontrunner.

Stoll has held elected office in the state since 1992, when he won a state House seat representing Jefferson County. He won a slot in the state Senate in 1998 and was easily re-elected in 2002.

Perhaps the strongest argument in Stoll’s favor in the race is the prevailing notion that he bears the imprimatur of the Gephardt Missouri political operation, a key element in the primary.

A Stoll aide did little to counter the idea that he is the chosen “Gephardt” candidate.

“There are very few coincidences in politics,” the aide said, pointing out that Stoll announced his candidacy the same day Gephardt allies made it known he would not run for a 15th term.

But Carnahan rejects the idea that Stoll has been given a private nod of support from the Gephardt machine.

“That is not correct,” he said. “I have spoken directly with the Congressman and with [Gephardt confidante] Joyce [Aboussie] and they have confirmed my understanding that they will not be involved in the 3rd district primary in any way.”

A state Democratic official added that Gephardt and his political allies are “focused much more on their own business” and are not likely to weigh in on the race.

In the end, the race may come down more to the ideological differences between Stoll and Carnahan than the strength of their respective political patrons.

On the abortion issue, Stoll is anti-abortion while Carnahan is pro-abortion rights.

Although Stoll’s position would typically handicap him in a Democratic primary, the 3rd district has a number of conservative, suburban St. Louis Democrats who may be in accord with Stoll.

“Senator Stoll is a better fit for that district,” said the Stoll aide. “Ideologically he simply fits better.”