Two authors of a bipartisan bill to revamp immigration laws said on Thursday they are hopeful most Senate Democrats and Republicans will support their White House-backed measure.

"It is very doable," Republican Senator John McCain of Arizona said of the prospects of attracting wide bipartisan backing. Democratic Senator Charles Schumer of New York agreed.

Speaking at a breakfast roundtable with reporters sponsored by the Christian Science Monitor, McCain and Schumer said their aim is to muster strong support in the Democratic-led Senate to help the measure's chances in the Republican-led House of Representatives.

"It is a balanced bill," Schumer said. "I'm optimistic it will pass."

McCain and Schumer drafted the comprehensive measure with six other senators, three Democrats and three Republicans. It would bolster border security, help provide low- and high-skilled workers for businesses and create an earned pathway to U.S. citizenship for 11 million undocumented immigrants.

McCain and Schumer said their optimism is based largely on an unprecedented coalition that supports their efforts, including business and labor, farmers and groups that represent agriculture workers and churches of all denominations.

Public opinion polls also show broad support.

McCain said once the bill reaches the full Senate, he expects weeks of debate and consideration of possible amendments.

"This is not the final bill," McCain said.

He said he and other co-sponsors are open to improving the measure but are ready to stand together to oppose any effort to undermine it.

McCain said he called Representative Paul Ryan, the 2012 Republican vice presidential nominee, on Wednesday to thank him for publicly voicing support in recent days for comprehensive immigration reform.

"I believe in it," McCain quoted Ryan as telling him.

(Reporting by Thomas Ferraro; Editing by Vicki Allen)