Two national environmental groups have such deep-seated dislike for Rep. Richard Pombo -- and see him as so vulnerable -- that they've made their maiden forays into congressional campaign politics to try to unseat him.

Their efforts have turned what might have been a snooze of a race into a nationally watched showdown to represent parts of San Joaquin, Contra Costa, Alameda and Santa Clara counties, and perhaps to help tip Congress' balance of power.

The new political arm of Defenders of Wildlife, the nation's fourth-largest environmental group, has spent more than a year, mobilized hundreds of volunteers and anted up almost $500,000 to oust Pombo, R-Tracy, a 14-year House veteran and Resources Committee chairman. The Humane Society of the United States' political arm entered the fray Sept. 15, capitalizing on its influence among Republican women.

Together, they've forced the Republican and Democratic parties essentially to admit the race for "Pombo Country" is a nail-biter.

"We wouldn't have started this in the first place if it didn't look like Pombo was going to lose," said Rodger Schlickeisen, executive director of Defenders and of its political arm, the Defenders of Wildlife Action Fund.

Pombo remains far ahead money-wise, with $1 million in his war chest at mid-October compared to $329,000 for Democratic challenger Jerry McNerney, who lost to Pombo by 22 percentage points in 2004.

But with a week to go, a chief sign that the race has tightened is the blizzard of money suddenly enveloping it.

President Bush came to raise money for Pombo on Oct. 3, and First Lady Laura Bush arrives Friday. The National Republican Congressional Committee has spent at least $1.3 million backing Pombo in recent months, while the Democratic Congressional Campaign Committee made its first, $112,000 ad buy last week while adding McNerney to its list of the nation's "strongest Democratic challengers."

Pombo campaign spokesman Brian Kennedy said the environmental groups undoubtedly have had an effect.

"When you spend $1 million tarnishing someone's reputation, using direct mail and radio and television ads, it does have an effect," he said. "There is no question that the money from the outside groups has made this a race that's even within 15 points."

McNerney claims his polls show a much closer race than that, and Schlickeisen said the gap has only tightened since his group's earliest polls -- in September 2005 -- showed Pombo would be vulnerable no matter who his foe.

Pombo's ongoing efforts to revamp the Endangered Species Act long have drawn environmental groups' ire, but his most recent attempt -- in 2005, when a bill he introduced before the Resources Committee was passed out of the House within days -- was the final straw, "the bellwether," Schlickeisen said.

The Defenders Action Fund now is active in 24 races nationwide, he said, with its involvement predicated upon whether a Republican voted for or against Pombo's bill.

Meanwhile, Pombo's animal rights record was so abysmal -- and his polling weak enough -- that the Humane Society's board smelled opportunity, said Humane Society Legislative Fund director Sara Amundson.

Of 300 congressional candidates and incumbents endorsed by the Society fund, 40 percent are Republicans; the group always has drawn Republican women's support in "a significant way," Amundson said, so its anti-Pombo effort has drawn attention. "We've put a race in play that may not have been in play."

Kennedy said neither group is a political novice -- especially Defenders of Wildlife -- and disputed the idea that opposing Pombo somehow helped the environment.

"They raise tens of millions of dollars every year from individuals who think they are protecting the environment," he said. "And then they turn around and spend the vast amount of that money, the overwhelming majority, to raise more money, to file lawsuits, to lobby and to engage in political campaigns."

DCCC spokeswoman Kate Bedingfield, wary of federal laws against coordination of independent expenditures, wouldn't discuss whether the environmental groups' heavy investment in the race played a part in the DCCC's decision to spend its resources elsewhere until just recently. It got involved in this race "as the national climate has trended even more in Democrats' favor over the past months," she said.

San Jose State University Political Science Professor Larry Gerston said the DCCC started out focusing only on the races it believed it had the very best chances to win, and expanded its spending to races such as this one ®MDRV¯"as this election has started to snowball and pick up some momentum for the Democrats, and new money has come in."

Gerston said the district's pricey geography -- straddling the San Francisco and Sacramento television and radio markets -- requires more bucks for a decent advertising bang, but he said it's unlikely the DCCC shorted McNerney because it had backed a different Democrat, Steve Filson, in the primary.

"These Democrats want to win, they're very much like the (Karl) Rove Republican machine -- they don't have time for sour grapes," he said. "A guy like (DCCC chairman) Rahm Emanuel, there's only one thing on his mind."

Contact Josh Richman at jrichman@angnewspapers.com.; Douglas Fischer at dfischer@angnewspapers.com.