House Speaker Nancy Pelosi is increasingly standing alone among top congressional Democrats in her unwavering insistence on a government-run health insurance plan. 

On all sides of her, other Democratic leaders -- including President Obama -- are casting the so-called "public option" as important but not essential, as conservatives assail it and moderate Democrats steadily back away from it. 

But even as fellow Democrats float alternatives, Pelosi is not budging. 

"I believe that a public option will be essential to our passing a bill in the House of Representatives," the California Democrat said Tuesday. "Right now, we will have a public option in our bill." 

Her insistence on the controversial component comes as hopes for it dim on the Senate side. Sen. Max Baucus, D-Mont., said Wednesday that a government-run insurance plan "cannot" pass the full Senate. In the Senate Finance Committee, the only relevant committee that has not yet approved its version of health care reform, Chairman Baucus is pitching a system of non-profit cooperatives. 

Independent Democratic Sen. Joe Lieberman, Conn., told FOX News he hopes Obama can convince Pelosi to tone her rhetoric down. 

"It will stop health care reform this year, and that would be a loss for everybody," said Lieberman, who opposes the public option. 

Democratic strategist Dan Gerstein said Pelosi is merely trying to represent the views of the liberal wing of the House and stake out a firm negotiating position in order to get the best deal possible for those members. Liberal members like Rep. John Conyers, D-Mich., and Rep. Maxine Waters, D-Calif., in recent days have bellowed about the absolute need for a public option. 

"To use a street term, she's trying to represent," Gerstein said of Pelosi. 

Some progressives have threatened to derail a bill with no public option, but Gerstein said even Pelosi realizes that she and the liberal wing may have to compromise in the end. He said the conflicting statements of other top Democrats reflect the "divisions within the Democratic family." 

Most notably, House Majority Leader Steny Hoyer, D-Md., is openly contradicting Pelosi. 

Hoyer said Tuesday he could vote for a package that doesn't include a government-run plan. 

"I believe the public option is an option. An option. An alternative. A choice," he said. 

And House Majority Whip Jim Clyburn, D-S.C., on Tuesday expressed openness to an alternative. 

"If you believe that we can have competition among insurance companies in this exchange without having a public option, then let's try it and see ... if you could do that on a reasonable basis," he said on MSNBC. 

He said a public option, in name, probably needs to be in the bill in order to pass the House, but he said that component could take different forms. 

"I don't think the public option has to be a mandate. I do believe that there are ways for us to get to a public option with it being a part," he said. Specifically, Clyburn mentioned a "trigger," or policy that would keep the public option on reserve in case insurance companies don't meet certain benchmarks. He also talked up an idea to set up "pilot programs" that would include a public option and co-ops. Those pilot programs would then be reviewed a few years down the road to determine whether they should be "mandated." 

Pelosi declined to respond to Clyburn's comments Tuesday. 

"I really can't speak to Mr. Clyburn's remarks," she said. "I do know that Mr. Clyburn is a strong supporter of a public option." 

The White House, in public, is still not giving up hope on a government-run plan. 

Obama, who is delivering a critical address to a joint session of Congress Wednesday night, will use the speech to press for a public option, according to a senior adviser.