By Lewis Krauskopf

NEW YORK (Reuters) - Health insurer Humana Inc <HUM.N> forecast profit to fall next year due in part to pressure on margins as it sees lower government reimbursement for its Medicare plans for the elderly.

Humana, which also posted a 65 percent jump in third-quarter profit on Monday, is one of the largest providers of Medicare plans so investors have been concerned about the hit to earnings as the government squeezes rates.

Humana shares fell 1.1 percent. Its 2010 forecast largely came in line with Wall Street expectations, when excluding for asset write-downs related to the end of a military contract, said Stifel Nicolaus analyst Thomas Carroll.

"They put it at a level in line with current expectations," Carroll said. "They talk about decent enrollment and revenue growth but also feeling some margin pain."

Humana forecast a big jump in Medicare Advantage enrollment -- adding as many as 240,000 members -- countered by a decline of about 140,000 members in its commercial plans serving employers, as the weak economy leads to fewer workers with coverage.

Humana expects an operating Medicare profit margin of about 5 percent next year, down from about 6.5 percent this year.

"They really managed to mitigate the margin hit a lot," said Sanford Bernstein analyst Ana Gupte. "And they're really dramatically increasingly Medicare enrollment."

Third-quarter net income was $301.5 million, or $1.78 per share, compared with $183 million, or $1.09 per share, a year earlier, when the company was hit by investment losses.

Analysts on average expected $1.77 per share, according to Thomson Reuters I/B/E/S.

Revenue rose 8 percent to $7.72 billion. Analysts expected $7.82 billion.

Humana is the first large health insurer to provide detailed 2010 forecasts, although it follows larger rival UnitedHealth Group <UNH.N> in expecting lower earnings per share next year.

WellPoint <WLP.N> and Aetna <AET.N> deferred giving a 2010 forecast until gaining more clarity on factors such as the state of the economy, the severity of the flu season and the outcome of health reform legislation.

Humana's forecast excluded any potential impact from the reform legislation under debate in Congress, such as an industry tax being considered. Continued...