Federal Reserve Chairman Ben S. Bernanke sent a strong signal Friday that the central bank is poised to expand its campaign to bolster the economy, describing in unusually chilling terms the depths of the nation’s unemployment problems.

In a widely anticipated speech here, Bernanke said economic growth is “far from satisfactory” and pledged that the Fed would be “forceful” in taking action to drive faster growth.

The tone of Bernanke’s remarks suggested, many economists say, that the central bank will launch a new round of economic stimulus when the Fed’s policy board meets in two weeks. It could embark on a new round of massive bond purchases, pushing record-low interest rates even lower and making it even cheaper for people to buy homes or refinance mortgages.

More likely, economists say, the Fed will take the more modest step of extending its plan to keep interest rates near zero for another year, from late 2014 to late 2015.

With Congress paralyzed and awaiting the outcome of the 2012 election, the Fed is carrying the entire burden of trying to keep the economy healthy in the face of many threats. But the central bank is also feeling more political pressure than perhaps ever before.

The Republican Party called for tightening oversight of the Fed at its national convention this week, and the party’s leadership has warned that the central bank’s actions have created dangers for the economy.

GOP presidential candidate Mitt Romney says he won’t reappoint Bernanke, and Republican lawmakers on Friday urged the Fed to refrain from taking any more action to stimulate economic activity.

Democrats have not been as outspoken. But lately, they have been putting additional pressure on the Fed to take measures to reduce unemployment.

In his speech, Bernanke argued that the nation’s high unemployment rate — 8.3 percent — represents a serious morale problem and also puts the long-term fortunes of the economy at risk.

“We must not lose sight of the daunting economic challenges that confront our nation,” Bernanke said, using strong language rare for the reserved former professor. “The stagnation of the labor market in particular is a grave concern, not only because of the enormous suffering and waste of human talent it entails, but also because persistently high levels of unemployment will wreak structural damage on our economy that could last for many years.”

“The Federal Reserve has acted to support economic growth and foster job creation,” he added, “and it is important to achieve further progress, particularly in the labor market.”

Bernanke hinted at, but offered no certainty of, action to come. His remarks suggest that he thinks the labor market might need another dose of medicine from the Fed.

In an analysis, JPMorgan’s chief U.S. economist, Michael Feroli, said, “It’s clear that the chairman, at least, has no intention of easing up on his resolve to attempt to foster recovery in the labor market.”

The urgent tone of Bernanke’s comments could leave investors disappointed if the Fed does not announce new stimulus measures at its Sept. 12-13 policymaking meeting. But investors seemed hopeful on Friday, with U.S. stocks up by about 0.6 percent.

Larry Lindsey, a participant in the conference and former senior economic adviser to President George W. Bush, said during a discussion that the central bank should show restraint.

“For our profession . . . modesty in what we express and what we think we can do is probably becoming,” he said.

In his speech, Bernanke implored policymakers to prevent the country from going over the “fiscal cliff” — the combination of deep cuts in federal spending and sharp tax hikes scheduled to take effect at the end of the year. Most economists think that those measures would tip the U.S. economy back into a recession — perhaps a deep one.

“Policymakers should take care to avoid a sharp, near-term fiscal contraction that could endanger the recovery,” he said. “Monetary policy cannot achieve by itself what a broader and more balanced set of economic policies might achieve. In particular, it cannot neutralize the fiscal and financial risks that the country faces.”

Bernanke’s speech seemed carefully designed to build on earlier suggestions that the Fed is ready to act.

After an early August policymaking meeting, the Fed declined to take new steps to stimulate growth but promised to do so if needed to help the economy. Minutes from that meeting, released last week, show that many of the officials at the session favored more action if the economy does not improve soon.

Next week, the government will release its unemployment numbers for August. A disappointing report — fewer than 100,000 or so jobs added to the economy — would likely tip the Fed toward stronger action. Robust data showing more than 150,000 jobs added could prompt the Fed to wait longer.

Also next week, the European Central Bank will announce details of the steps it is taking to alleviate the continent’s financial crisis, a major drag on the U.S. economy. If the ECB takes dramatic action, it might reduce the incentive for the Fed to act.

Any steps taken by the Fed’s policy board might have only a modest impact on the country’s economic health. Extending the plan for ultra-low interest rates through 2015 would reduce unemployment by only 0.1 or 0.2 percentage points, according to economists who track the Fed. By contrast, the emergency measures taken by the Fed during the financial crisis had a dramatic impact.

Most of Bernanke’s comments Friday represented a spirited defense of the Fed’s actions over the past four years to protect the economy. These included bringing short-term interest rates to historic lows and launching a range of unconventional programs to try to foster growth.

Bernanke said he thought that the central bank’s actions had provided significant support to the economy. He said they may account for half of the 4 million private-sector jobs added since hiring hit a low.

Reacting to Bernanke’s speech on Friday, Sen. Bob Corker (R-Tenn.), a member of the Senate banking committee, argued that action from Congress, not from the Fed, would best help the economy.

“Today’s speech highlights the desperate need for policymakers to meaningfully address the underlying problems in our economy,” he said. “These policies from Congress, not more short-term stimulus from the Fed, are the ingredients necessary for restoring growth in the American economy.”

Sen. Charles E. Schumer (D-N.Y.) argued that Bernanke should do more and ignore criticism from the right.

Any major action before Election Day could plunge the Fed even deeper into the political campaign. That’s the kind of attention that Bernanke and the Fed don’t want.