Managed-care stocks tumbled and hospital shares climbed Thursday as an analysis of the Senate Finance Committee's health-reform bill increased chances that the measure, which one analyst called "onerous" for health insurers, will advance.

Contributing to the managed-care sell-off, apparently, were House Speaker Nancy Pelosi's comments expressing interest in exploring a windfall-profit tax on insurers to fund an expansion of health coverage.

The nonpartisan Congressional Budget Office late Wednesday predicted the latest version of the Senate Finance Committee bill would cost $829 billion over 10 years, expand health insurance coverage to most Americans and reduce the federal deficit. The panel plans to vote on the bill early next week.

Wall Street analysts were skeptical about some of the CBO's assumptions, and a health-insurance trade group, the Blue Cross and Blue Shield Association, said the scorecard understated the bill's "significant weakening" of a proposed mandate that every individual become insured.

WellPoint Inc. (WLP), the largest managed-care company by membership, closed down 6.2%, or $2.94, at $44.72. UnitedHealth Group Inc. (UNH), the largest by revenue, Aetna Inc. (AET), Humana Inc. (HUM) and Cigna Corp. (CI) traded down by approximately 3.6% to more than 5%.

Hospital operators, expected to receive a boost from expansion of health coverage to more patients, saw stocks rise. Tenet Healthcare Corp. (THC) shares closed up nearly 5%, or 28 cents, at $5.95, while Universal Health Services Inc. (UHS), Health Management Associates Inc. (HMA), LifePoint Hospitals Inc. (LPNT) and Community Health Systems Inc. (CYH) climbed roughly in the 2.4%-to-4.4% range.

The CBO score increases the probability that the bill could pass the Senate with a filibuster-proof 60 votes, according to Wells Fargo hospital analyst Gary Lieberman, who said the measure should increase the percentage of insured individuals from 83% today to 94% in 2015.

Managed-care analysts disagreed with several aspects of the CBO assessment and didn't like the look of the bill for health insurers.

"We continue to view the ... bill as quite onerous for managed care," Deutsche Bank's Scott Fidel said.

Analysts noted that the CBO assumed Medicare physician fees will be cut by 25% next year, which they called unlikely.

"The CBO score matters more than whether the score itself is realistic," Wells Fargo managed-care analyst Matt Perry said. "We expect Republicans to attack the credibility of the score along these lines, but we're skeptical that they'll gain much traction."

The bill, assuming it passes, will have to be merged with a measure from another Senate panel and reconciled with House legislation.

The CBO doesn't seem to see a risk of significant adverse selection - in which riskier or sicker people seek coverage - from weakened provisions mandating individual coverage, Goldman Sachs analyst Matthew Borsch said. "However, the CBO analysis does nothing to allay our own concern over the adverse selection risk as it may impact managed-care companies in the individual and small-group insurance business."

Borsch said Congress could give final approval to health-care overhaul legislation by mid-December.

The Blue Cross and Blue Shield Association, meanwhile, said amendments made to the bill in the Senate Finance Committee "eviscerated the individual mandate.... This is likely to result in millions of people foregoing coverage. A weak mandate, as included in the amended Senate Finance Committee bill, would encourage people to wait until they are sick to purchase coverage. This will drive up premiums for everyone."

The bill doesn't include a provision for a public health plan to compete with private insurers, a proposal that the health insurance industry has been fighting.

-By Dinah Wisenberg Brin, Dow Jones Newswires; 215-656-8285;

(MarketWatch editor Laura Mandaro contributed to this article.)