JACKSON HOLE, Wyo. — Federal Reserve Chairman Ben S. Bernanke, decrying the suffering caused by unemployment of more than 8 percent and defending his unprecedented policies, said Friday that more bond purchases are an option as central bankers weigh further steps to spur growth.

“The costs of nontraditional policies, when considered carefully, appear manageable, implying that we should not rule out the further use of such policies if economic conditions warrant,” Bernanke said today in a speech to central bankers and economists at an annual forum in Jackson Hole.

Stocks and Treasuries climbed as investors increased bets the Fed will expand its record stimulus. Bernanke, speaking two weeks before the next meeting of the Federal Open Market Committee, said long periods of high unemployment produce “enormous suffering and waste of human talent” and also risk causing “structural damage on our economy that could last for many years.”

“Given Bernanke’s remarks, additional monetary stimulus seems more likely than it did,” said Mark Vitner, a senior economist at Wells Fargo Securities in Charlotte, N.C. “It is not 100 percent, and the timing is an even greater question.”

Bernanke’s 24-page speech at the Kansas City Fed’s symposium reviewed the Fed’s policy actions through the financial crisis and use of nontraditional policy tools such as communication and $2.3 trillion in outright bond purchases, concluding that they have been effective in boosting growth and improving financial conditions.

Studies have shown that the Fed’s asset purchases have been “economically meaningful” after they “significantly lowered long-term Treasury yields” and boosted stocks, which affects consumption and investment decisions, Bernanke said.

Even so, “we have seen no net improvement in the unemployment rate since January,” Bernanke said. “Unless the economy begins to grow more quickly than it has recently, the unemployment rate is likely to remain far above levels consistent with maximum employment for some time.”

Bernanke concluded by repeating the FOMC’s last statement that the central bank “will provide additional policy accommodation as needed” to spur growth.

Policymakers at their Aug. 1 meeting were moving toward additional action, according to minutes released last week. Many members of the panel said more stimulus will be needed “fairly soon” unless the recovery shows signs of a “substantial and sustainable strengthening.”

Since the meeting, data on housing, manufacturing and retail sales have exceeded expectations.

Retail sales rose 0.8 percent in July, the most in five months, and sales of existing homes rose from an eight-month low. Consumers increased spending for the first time in three months, government data showed yesterday, and retailers such as Gap and Macy’s posted same-store sales this month that topped analysts’ estimates.

The Standard & Poor’s 500 Index climbed 11 percent this year through Thursday as company earnings beat forecasts and investors speculated that the Fed will take steps to support the expansion. About 71 percent of companies in the index reported results that exceeded analysts’ estimates, according to data compiled by Bloomberg.

The yield on the benchmark 10-year Treasury has fallen from a 2012 high of 2.38 percent in March as investors sought the safety of U.S. debt. A report Friday showed consumer confidence rose more than projected to the highest level in three months.

Recent signs of strength in the economy may not be enough to satisfy Fed policymakers whose mandate from Congress requires them to aim for maximum employment and stable prices.

Gross domestic product expanded at a 1.7 percent annual rate in the second quarter, slowing from 4.1 percent in the final three months of last year. Employers probably added 127,000 jobs in August, down from 163,000 a month before, according to the median forecast in a Bloomberg News survey of economists.

At the same time, inflation is falling below the Fed’s goal of 2 percent. The measure watched by central bankers, known as the personal consumption expenditures price index, slowed to a 1.3 percent annual increase in July, the least since October 2009.

Cooling growth leaves the world’s biggest economy more vulnerable to fallout from the debt crisis in Europe and the so-called fiscal cliff in the U.S., the $600 billion of tax increases and spending cuts that will take effect automatically at the end of the year unless Congress acts.

Budget cuts at all levels of government have “become an important headwind for the pace of economic growth,” Bernanke said today. In addition, “a major source of financial strains has been uncertainty about developments in Europe.”

The minutes of their last meeting showed policy makers considered extending the time horizon the Fed expects to keep its benchmark interest rate low.

Since January, the Fed has said economic conditions would likely warrant keeping the rate “exceptionally low” through at least late 2014. The rate has been kept close to zero since December 2008.

Policymakers could also opt for a third round of large- scale asset purchases, known as quantitative easing, intended to push long-term borrowing costs lower.

The steps are among the unorthodox policy tools wielded by Bernanke, a 58-year-old former Princeton professor, as he sought to pull the nation out of its worst recession since the Great Depression and then to ensure a lasting recovery.

Bernanke, a student of the Depression, has presided over what the economist William White, a former member of the Bank for International Settlements’ executive committee, calls “one of the greatest economic experiments of all time.”

Three years into the expansion, Bernanke has tried to nudge the economy onto a path of stronger growth to boost hiring. The FOMC on June 20 extended a program, known as Operation Twist, that replaces short-term notes in its portfolio with longer-term assets in an effort to further suppress longer-term interest rates.

The Fed chairman’s unprecedented use of the central bank’s powers – which also involved the rescue of Bear Stearns Cos. and American International Group Inc. during the financial crisis – has become a contentious issue in an election year.

Mitt Romney, the Republican presidential candidate, told the Fox Business Network on Aug. 23 that he wouldn’t reappoint Bernanke, raising questions about the succession more than a year before Bernanke’s term expires in January 2014. The 2012 Republican platform calls for an audit of the Fed’s monetary policy.

“Criticism is fair game, but this is like political football,” said Mark Gertler, a New York University economist and research collaborator with Bernanke. “Years from now, people who will look back are going to thank God we had Bernanke as chairman over this period and that he was able to keep the focus on the job and conduct responsible monetary policy.”

Bernanke’s speech at Jackson Hole in 2010 signaled a willingness to undertake additional unconventional policies to ward off weak growth and the risk of deflation.

At its meeting the following November, the Fed announced it would embark on a second round of bond purchases. The Standard & Poor’s 500 Index rallied 18 percent beginning Aug. 27, 2010, when Bernanke spoke, through the year end.

While Eric Rosengren, president of the Federal Reserve Bank of Boston, and Charles Evans, head of the Chicago Fed, have called for additional stimulus since the last FOMC meeting, St. Louis Fed President James Bullard said in a Bloomberg Television interview today that he “would like to see some more data before taking really big action.”