A tentative thumbs-up. That's the assessment from economists, who have offered mainly positive reviews of President Barack Obama's $447 billion plan to stimulate job creation. Some predict it would put hundreds of thousands of people back to work next year, mainly because a Social Security tax cut for workers would be deepened and extended to small businesses.

"Payroll tax cuts are very powerful," says Allen Sinai, chief economist of Decision Economics. "They provide a boost to direct income and, in turn, spending, which is important to growth." Mark Zandi, chief economist at Moody's Analytics, estimates that the president's plan would boost economic growth by 2 percentage points, add 2 million jobs and reduce unemployment by a full percentage point next year compared with existing law.

The dismal state of the economy is the main reason many companies are reluctant to hire workers, and few executives are saying that President Obama's jobs plan -- while welcomed -- will change their minds any time soon. That sentiment was echoed across numerous industries by executives in companies big and small on Friday, underscoring the challenge for the Obama administration as it tries to encourage hiring and perk up the moribund economy.

The plan failed to generate any optimism on Wall Street as the Standard & Poor's 500-stock index and the Dow Jones industrial average each fell about 2.7 percent. As President Obama faced an uphill battle in Congress to win support even for portions of the plan, many employers dismissed the notion that any particular tax break or incentive would be persuasive. Instead, they said they tended to hire more workers or expand when the economy improved.

Democrats are expressing growing alarm about President Obama's re-election prospects and, in interviews, are openly acknowledging anxiety about the White House's ability to strengthen the president's standing over the next 14 months.

Elected officials and party leaders at all levels said their worries have intensified as the economy has displayed new signs of weakness. They said the likelihood of a highly competitive 2012 race is increasing as the Republican field, once dismissed by many Democrats as too inexperienced and conservative to pose a serious threat, has started narrowing to two leading candidates, Mitt Romney and Rick Perry, who have executive experience and messages built around job creation.

And in a campaign cycle in which Democrats had entertained hopes of reversing losses from last year's midterm elections, some in the party fear that Mr. Obama's troubles could reverberate down the ballot into Congressional, state and local races. ...

But a survey of two dozen Democratic officials found a palpable sense of concern that transcended a single week of ups and downs. The conversations signaled a change in mood from only a few months ago, when Democrats widely believed that Mr. Obama's path to re-election, while challenging, was secure.