American employers have a variety of job vacancies, piles of cash and countless well-qualified candidates. But despite a slowly improving economy, many companies remain reluctant to actually hire, stringing job applicants along for weeks or months before they make a decision.

If they ever do.

The number of job openings has increased to levels not seen since the height of the financial crisis, but vacancies are staying unfilled much longer than they used to — an average of 23 business days today compared to a low of 15 in mid-2009, according to a new measure of Labor Department data by the economists Steven J. Davis, Jason Faberman and John Haltiwanger.

Some have attributed the more extended process to a mismatch between the requirements of the four million jobs available and the skills held by many of the 12 million unemployed. That’s probably true in a few high-skilled fields, like nursing or biotech, but for a large majority of positions where candidates are plentiful, the bigger problem seems to be a sort of hiring paralysis.

“There’s a fear that the economy is going to go down again, so the message you get from C.F.O.’s is to be careful about hiring someone,” said John Sullivan, a management professor at San Francisco State University who runs a human resources consulting business. “There’s this great fear of making a mistake, of wasting money in a tight economy.”