WASHINGTON - California Rep. Richard Pombo is closer than ever to his longtime goal of rewriting the Endangered Species Act to add rights for property owners.

But his success has helped bring the Republican congressman from Tracy his greatest political test since he first came to Washington 14 years ago.

Pombo's aggressively conservative leadership as chairman of the House Resources Committee, where he's also supported drilling for oil and privatizing public lands, has drawn him a prominent GOP primary opponent, former Rep. Pete McCloskey, and well-funded opposition from environmentalists.

If he wins the June 6 Republican primary, he would face one of several determined Democratic challengers who are competing to face him.

At the same time, Pombo, 45, has been touched by the corruption scandals sweeping Congress. He also is running in a district that was reconfigured after the 2000 census to add San Francisco Bay area voters more liberal than his longtime San Joaquin Valley constituents.

Pombo said he's not worried.

"I'm getting a lot more attention than I have in the past, but it doesn't change the registration numbers in the district, it doesn't change how conservative or liberal people are," said the cowboy-hat-wearing cattle rancher.

His opponents, however, hope circumstances are lining up in their favor. While ousting an entrenched and well-funded incumbent remains a longshot, they believe that if they ever had a chance to take Pombo down, this is the year.

"We feel that Richard Pombo has put himself into a much more vulnerable position than anyone would have thought he'd be in," said Bill Burton, spokesman for the Democratic Congressional Campaign Committee, the fundraising arm for House Democrats.

Republicans outnumber Democrats 44 percent to 37 percent among voters in Pombo's 11th Congressional District, and Pombo has raised about five times as much money as his nearest opponent in either party.

Pombo comes from a Portuguese immigrant ranching family that's well-known in his hometown of Tracy, where many voters appreciate his advocacy for private property rights. Signs for his uncle's Pombo Real Estate dot country roads.

"I'll be lucky if I win," said McCloskey, 79, who represented the San Francisco peninsula area from 1967 to 1982 and is challenging Pombo in the Republican primary.

But McCloskey added: "If I don't win, it will stand as a stamp of approval for what is going on in Washington these days."

McCloskey is one of an increasingly rare breed of Republican moderates, an original author of the Endangered Species Act and a sponsor of the first Earth Day. He believes so strongly that Pombo should be removed that he came out of retirement and moved 90 miles south into the district after failing to recruit any other Republican moderate to run.

McCloskey has traveled the district in an RV emblazoned "Real Republican Values Express" and has made ethics the central theme of his campaign against Pombo, whom he calls "an embarrassment."

McCloskey highlights questions about Pombo's use of public funds - including using taxpayer money to rent an RV for a family tour of national parks - as well as the incumbent's alliance with former House Majority Leader Tom DeLay and ties to disgraced lobbyist Jack Abramoff. DeLay helped Pombo leap over several more senior Republicans to get his chairmanship in 2003; Abramoff and some of his clients donated heavily to Pombo.

Pombo rebuts the criticism. He says the RV trip was business, and defends DeLay, who gave up his majority leader post after being indicted on campaign finance charges. Pombo also says he barely knew Abramoff and that his support for an Indian tribe represented by Abramoff was appropriate. Pombo donated to charity the $7,000 he got directly from Abramoff but hung onto tens of thousands more he took from the lobbyist's clients, contending it was properly received.

"I have never broken any rules in the House of Representatives. I have never broken any laws. All I have done is fight for what is right," Pombo declared during a Tracy candidate forum with McCloskey and a third Republican candidate, Tom Benigno, on May 15.

Pombo and his aides dismiss McCloskey, who supported John Kerry for president in 2004 and is getting campaign help from Democrats, as a carpetbagger and Democratic Party tool.

"He doesn't understand anything about the district, has really no interest in any local issues at all, and he's running around getting some good attention right now, so I think he's enjoying that," Pombo said.

On the Democratic side, the leading contenders are first-time candidate Steve Filson, a United Airlines pilot, and wind engineer Jerry McNerney, who ran against Pombo in 2004. Filson is getting help from national Democrats, including House Minority Leader Nancy Pelosi of San Francisco, while McNerney is picking up grassroots support, including the state Democratic Party's endorsement.

Pombo's challengers are benefitting from environmentalists' extreme disdain for him. Defenders of Wildlife and the League of Conservation Voters have made defeating him a top political goal. They're spending hundreds of thousands of dollars on radio ads and mailers accusing him of being in the energy industry's pocket and trying to roll back environmental laws and gut landmark species protections.

Pombo scoffs at such claims, contending environmental groups attack him partly to raise money to keep themselves in business.

After years of trying, Pombo got the House of Representatives to pass his endangered species bill in September, although chances of Senate action this year are dimming. The legislation would stop the federal government from designating habitat for plants and animals where protections are in place, and require compensation to landowners if species protections interfere with development plans.

Environmentalists say Pombo's proposals would have made it impossible to protect famous species such as the bald eagle.

Pombo disagrees. And far from avoiding the issue in his campaign, he has made it the focus of radio and television ads that cite examples - disputed by environmentalists - of unreasonable species protections interfering with levee construction and troop training.