WASHINGTON -- As the Senate on Thursday began what promises to be a bitter, lengthy battle over the future of health care in America, the issues of taxes, abortion, affordability and federal deficits emerged as key points of debate.

Senate Democratic leaders expect the first test vote on their new $848 billion, 2,074-page health care overhaul bill will come on Saturday evening. Although Democrats are likely to get the 60 votes they need to move forward with the debate, the outcome is uncertain. Should the measure pass that initial test, lawmakers made it clear Thursday that they're ready for weeks of political warfare.

Democrats framed their mission in heroic terms.

"This is about the woman with high cholesterol, or the man with heart disease, or the child with hay fever who can't get help," said Senate Majority Leader Harry Reid, D-Nev. "That's why we're stopping insurance companies from deciding they'd simply rather not give health care to the sick."

Republicans countered that the Senate bill would create more bureaucracy and run up the federal debt, and would hardly make health care more affordable. "We don't need a 2,000-page bill," said Sen. Lamar Alexander of Tennessee, the Republican conference chairman. "We need to take it step by step in the right direction to cut health care costs."

The bill would require most legal U.S. residents to obtain health coverage and would create insurance exchanges, or marketplaces, where people could shop for policies and rates. It would create a new federal insurance alternative, or public option, for most people who can't get private insurance. The nonpartisan Congressional Budget Office estimates that 94 percent of the public would obtain coverage by 2019, up from the current 83 percent.

Insurers would have to accept all applicants and couldn't deny coverage because of pre-existing conditions. States could opt out of the public system.

In the weeks ahead, though, senators plan to offer amendments on almost every piece of the bill. Thursday, some of the key questions surrounding the bill and its future included:

--Can a compromise be reached on abortion?

The House agreed to tough restrictions on access to abortion, but the Senate bill has language preferred by abortion rights supporters. Some Republican abortion foes are insisting that Saturday's procedural vote should be seen as a test of abortion sentiment. "This is a critical pro-life vote," said Sen. Mike Johanns, R-Neb.

--Will the bill make coverage more affordable?

Supporters argue that competition among insurers, as well as allowing the government to negotiate public-plan reimbursement rates, should lower costs.

The CBO analysis, however, warned that the public plan would result in "premiums that were somewhat higher than the average premiums for the private plans in the exchanges." One reason, it said, is that the government option would "attract a less-healthy pool of enrollees."

--Will senators accept tax increases?

Republicans have for years resisted most big tax increases and won political success for doing so. The bill's excise and Medicare taxes alone would generate $203 billion over 10 years, the CBO said. There also would be a series of smaller taxes, such as a new 5 percent tax on elective cosmetic surgery.