Washington - If the Senate doesn't pass a bill to cut global warming, Democratic Sen. Barbara Boxer says, there will be dire results: droughts, floods, fires, loss of species, damage to agriculture, worsening air pollution and more.

    She says there's a huge upside, however, if the Senate does act: millions of clean-energy jobs, reduced reliance on foreign oil and less pollution for the nation's children.

    Boxer is engaged in her biggest sales job ever. The stakes couldn't be higher as she faces one of the toughest high-profile acts of her lengthy career: getting Congress to sign off on historic legislation to lower greenhouse-gas emissions.

    "For Barbara Boxer, it's both the opportunity and a challenge of a lifetime," said Frank O'Donnell, the president of Clean Air Watch.

    As the Senate's top-ranked environmentalist, Boxer heads the influential committee that began hearings on the issue this week. She's aiming to get her panel to pass a bill by the end of September. For months now, she's been meeting with senators one on one and hosting a group of about 30 senators for "Tuesday at 12" meetings to develop a strategy to win 60 votes, enough to overcome a Republican filibuster.

    With a House of Representatives bill already approved, all eyes are on Boxer, who must overcome plenty of skepticism on Capitol Hill among her fellow Democrats.

    "It's going to be a tough slog, but I'm excited about it. . . . I know that my Republican colleagues are going to try to do everything to stop it and distort it," Boxer said Friday in an interview.

    Last year, Boxer's standalone climate-change bill fell to defeat, but there's a new strategy this year that will make it harder for senators to reject it. Six committees — Environment and Public Works, which Boxer heads, Finance, Commerce, Energy, Agriculture and Foreign Relations — will have jurisdiction over the bill. Those committee heads have been meeting for months with Senate Majority Leader Harry Reid of Nevada, who'll help combine their work into one massive bill this fall.

    Boxer said the approach was unlike any she'd experienced since she joined the Senate in 1993, and she predicted that it will simplify passage.

    "It's a different dynamic, and it will make it easier," she said in the interview. "There will be so much in this bill. There will be investments in transportation. There will be great opportunities for agriculture. There will be great incentives for energy efficiency. There will be so much in there. There will be help for areas that need flood control. It should have a broader appeal. Having said that, it's all difficult."

    While vote counts vary, most observers say that the bill's fate will lie with 15 or so Democratic moderates, many of whom fear that a vote for climate-change legislation could hurt their re-election chances. Boxer is trying to round up some Republican votes to offset opposition from the likes of Democratic Sens. Mary Landrieu of Louisiana and Ben Nelson of Nebraska.

    Boxer has been telling audiences for years that Congress must act, and that it will. After years of battling with the Bush administration, Boxer figures she has the best odds ever of getting a bill signed into law.

    It still won't be easy, however.

    Sen. James Inhofe of Oklahoma, the top-ranked Republican on the environment committee, predicts that Boxer will fail. He said the public would see the legislation as a large tax increase once people understood that they'd ultimately bear the costs of any bill that forced companies to reduce global-warming emissions.

    "Once the American public realizes what this legislation will do to their wallets, they will resoundly reject it," Inhofe said Tuesday at a hearing.

    Boxer said the legislation wouldn't include any new taxes, and she's portraying Republican opponents as obstructionists.

    "This is consistent with a pattern of 'No. No, we can't. No, we won't,' " Boxer said. "I believe that this committee, when the votes are eventually taken on our bill, will reflect our president's attitude, which is 'Yes, we can, and yes, we will.' "

    Aides say that Boxer, who's spent her political career focused on environmental issues, is keenly aware that this is her big moment, a chance to cement a legacy that would include passage of legislation with a worldwide impact. Three more committee hearings are set for next week, and a vote by the full Senate could come as early as October.

    Boxer has been working closely with top White House aides and Reid, a close ally, to figure out a way to pass the bill. To reach out to farm-state and coal-state senators, she's enlisted a team of lieutenants: Democratic Sens. John Kerry of Massachusetts, Amy Klobuchar of Minnesota, Sheldon Whitehouse of Rhode Island and Thomas Carper of Delaware, among others.

    While Boxer has yet to introduce specifics of her bill, it's expected to build on a House plan that was approved 219-212 last month, which would set the first enforceable limits on global warming pollution. The cap on emissions would reduce them by 17 percent below 2005 levels by 2020 and 83 percent below 2005 levels by 2050. Among other things, it also would require that the nation get 20 percent of its electricity from renewable energy in 2020 and set energy-saving standards for buildings, appliances and industries.

    The Obama administration is expected to lobby hard on Boxer's behalf, as was evidenced by this week's hearings. The administration sent four of its top-level appointees to make the case for the bill: Energy Secretary Steven Chu, Interior Secretary Ken Salazar, Agriculture Secretary Tom Vilsack and Lisa Jackson, the head of the Environmental Protection Agency.

    Boxer has plenty of support from most environmental groups, but she's bound to feel the heat as she begins compromising to win votes. Greenpeace, for example, and others opposed the House bill, saying that it had been weakened too much to appease farm-state interests.

    O'Donnell said that Boxer would face those same pressures.

    "That is going to be one of the real challenges for Boxer," he said. "How do you ensure the integrity of the program while bringing along farm-state senators to your side?"