The nation's employment engine remains stubbornly stuck in neutral, with the economy adding just 115,000 jobs in April while the unemployment rate declined slightly to 8.1 percent, the U.S. Labor Department reported Friday.

"We are likely seeing continued uncertainty over the state of the economy," said Joel Naroff, chief economist with Naroff Economic Advisors in Bucks County. "As for the payroll numbers, they were downers."

Economists say employment must expand by 100,000 to 150,000 jobs a month to accommodate population growth.

With the employment numbers, stocks plunged on Wall Street. The Standard & Poor's 500 index and the Nasdaq composite closed out their worst weeks of the year. The Dow Jones industrial average closed down 168 points, finishing at 13,038 Friday, for its second-worst weekly decline this year.

Nationally, manufacturing, retailing, and professional and business services all added jobs in April, as did education and health services. But government funding continued to drop, with 10,700 jobs lost in public education. Construction, ground passenger transportation, and leisure activities also showed losses.

Like most analysts, Ryan Sweet, a senior economist at Moody's Analytics in West Chester, cautioned that not too much should be read into any one number in any one month.

And that's particularly true this year, he said, when the unseasonably warm winter may have overwhelmed the algorithms the Labor Department uses in its reports to compensate for seasonal patterns.

"It was such weird weather," he said.

Here's an example: There were 171,000 more jobs in construction in April than in March, but on the same chart, five columns to the right, the Labor Department reported that there were actually 2,000 fewer jobs. How can that be?

Typically, the department figures out how many jobs there would normally be in construction in any given month, with more jobs, obviously, in warm-weather months. Most reports, however, quote the seasonally adjusted data, which incorporate a calculation comparing that month's jobs with what's normal.

The only problem was that this winter was anything but normal, and Sweet thinks the statistics are still catching up.

He said he thinks the January and February "job markets were not as good as they appeared" because they were skewed upward because of the weather. "In the long run, it's still a very weak job market," he said.

One measure of that is the employment-population ratio, comparing the number of people with jobs to the number of people in the population (except for those in the military or in jail.)

In April, 58.4 percent of the civilian population was employed, unchanged from April a year ago. In 2007, the year the recession began, the number averaged 62.9.

Yet, in general, compared with the statistics from a year ago, employment has clearly improved, although not dramatically, as Friday's report showed.

The ranks of the employed have grown by 2.2 million, while the number of unemployed has dropped by nearly 1.8 million, to 12.5 million.

"Today's employment report provides further evidence that the economy is continuing to heal from the worst economic downturn since the Great Depression, but much more remains to be done to repair the damage caused by the financial crisis and the deep recession," said Alan B. Krueger, chairman of the White House Council of Economic Advisers.

In Pennsylvania, where the unemployment rate was 7.5 percent in March, the improvement means that, effective the week ending May 12, the state's long-term jobless will no longer be able to receive the last 13 weeks of unemployment benefits.

Earlier in the recession, unemployed people were able to receive as many as 99 weeks of benefits, but as the economy has gotten better, some weeks already have been trimmed. After the most recent cut, Pennsylvania's unemployed will be able to receive a maximum of 73 weeks of benefits, down from 86 weeks.

In New Jersey, where March's unemployment rate was 9 percent, unemployed people can receive a maximum of 99 weeks of benefits.

This article includes information from the Associated Press.