Confidence among small U.S. business owners hit a four year-high in January and many are having trouble filling vacant positions, according to a survey released on Tuesday that added to signs the economic recovery is strengthening.

The National Federation of Independent Business said its optimism index rose to 93.9 in January, the highest level since December 2007 when the recession started. It was the fifth straight month of gains. The index in December had a reading of 93.8.

The survey is the latest evidence indicating the economy got off to a fairly solid start in 2012. U.S. employers added 243,000 new workers to their payrolls in January and the unemployment rate dropped to a three-year low of 8.3 percent.

Other data on the manufacturing and services sectors have also been fairly upbeat, leading some economists to temper their expectations for a sharp slowdown in first-quarter growth.

The NFIB survey, which was conducted through Jan. 31, showed layoffs at their lowest level since October 2007.

Forty-one percent of respondents said they hired or tried to hire new workers in the past three months, but 31 percent reported few or no qualified applicants for the positions.

"The increase in the percent of owners with hard-to-fill job openings indicates that job markets are tightening somewhere," the NFIB said in a statement.

The survey also found an improvement in the spending picture and sales volumes. Of the 2,155 respondents, 18 percent reported raising their average selling prices in the past three months, up a point from the December survey.

About 17 percent reported price reductions, down one point, while 23 percent plan to raise average prices in the next few months, and 3 percent plan reductions.

"With some evidence that spending has picked up, some of these price hikes might stick," the NFIB said.