OMAHA, Neb. – Billionaire Warren Buffett wants Americans to be optimistic about the country’s future but wary about borrowing money and the games public companies play with profit numbers they report.

Buffett said in his annual letter to Berkshire Hathaway shareholders Saturday that he still believes America’s best days are ahead.

“Commentators today often talk of ‘great uncertainty.’ But think back, for example, to December 6, 1941, October 18, 1987, and September 10, 2001,” Buffett wrote, referring to the days before the Pearl Harbor attack, a stock market crash and terrorist attacks in the U.S. “No matter how serene today may be, tomorrow is always uncertain. Don’t let that reality spook you.”

He said a housing recovery will likely begin within the next year, which would help the economy and several Berkshire subsidiaries.

Buffett’s letter detailed how the acquisition of Burlington Northern Santa Fe railroad, better results at Berkshire’s other subsidiaries and a $1.9 billion paper gain on investments and derivatives combined to boost the company’s net income by 61 percent to $12.97 billion in 2010.

The letter was full of good news for Berkshire investors because nearly all of its businesses, except the ones linked to housing, performed well, said Glenn Tongue, a managing partner at T2Partners investment firm.