WASHINGTON » Job openings are rising modestly, a sign that employers may step up hiring soon.

But rising openings in the past year haven’t reduced unemployment, heightening concerns that the unemployed might lack the skills to fill the jobs that are coming available. If companies have openings but can’t find qualified workers, that will make it even harder to lower the unemployment rate.

Some economists argue that the broader problem is that the economy just isn’t generating enough jobs.

The number of jobs advertised rose by 6.2 percent to 3.04 million in July, according to the Labor Department’s latest data. That’s the highest total since April, when temporary census hiring inflated that month’s figure. But even with the increase, total openings remain far below the 4.4 million that existed in December 2007, when the recession began.

Openings have risen 30 percent since July 2009, when they fell to their lowest level on records dating to 2000. Yet the unemployment rate has actually ticked up during that period, from 9.4 percent a year ago to 9.6 percent last month. Private employers added a net total of only 67,000 jobs in August, the government said Friday. That’s below the roughly 100,000 jobs a month the economy needs just to keep up with population growth.

Some analysts say that means factors other than a lack of hiring are keeping the jobless rate high. Workers may not have the expertise the new jobs require. Or falling home prices may make it harder for the unemployed to sell their homes and move to where jobs are available.

Narayana Kocherlakota, president of the Federal Reserve Bank of Minneapolis, said such mismatches could account for as much as 2.5 percentage points of the unemployment rate.

"Firms have jobs but can’t find appropriate workers," he said in a speech yesterday in Missoula, Mont. "The workers want to work, but can’t find appropriate jobs."

This limits what the central bank can do to reduce unemployment, Kocherlakota said. In a similar speech last month, he said, "The Fed does not have a means to transform construction workers into manufacturing workers."

Many private recruiters say they are having a hard time finding the right people for jobs that are available. A survey by the Corporate Executive Board of company recruiters found that most are struggling to hire qualified job seekers. More than 80 percent said that fewer than half their applicants are qualified, even though the number of unemployed has surged since the recession began.

That’s partly because many of those who have lost their jobs in the downturn are relatively low-skilled, according to Jean Martin, an executive director at the Corporate Executive Board. Those with a high school education or less have a higher unemployment rate than those with college degrees. And the gap widened during the downturn.

Some economists say the skills and geographic mismatches aren’t the biggest obstacle for jobseekers. The overall weakness of the economy is the main problem, they say.

"The same pattern has been seen in previous downturns," said Lawrence Katz, a Harvard economist. "When the economy starts growing again … firms start taking chances on people and training them."