A TV screen on the floor of the New York Stock Exchange shows Federal Reserve Chair Janet Yellens first news conference, in Washington D.C. on Wednesday. (Richard Drew/AP)

The Federal Reserve began laying the groundwork Wednesday for the first increase in interest rates since the Great Recession upended the economy.

The nation’s central bank said it will consider a broad swath of indicators to determine the moment of liftoff, including job market data, inflation expectations and financial developments. The official statement was a retreat from the blanket assurances that rates would remain untouched, which have dominated the Fed’s message for the past five years. Instead, the debate has shifted to how much longer the Fed should wait before pulling the trigger.

Speaking at a news conference Wednesday, Fed Chair Janet L. Yellen cast the shift as merely a change in semantics, not policy. The central bank’s target for interest rates has been at zero since 2008, and most Fed officials think the first increase will occur next year.

“Monetary policy will be geared to evolving conditions in the economy,” Yellen said. “And the public does need to understand that as those views evolve, the committee’s views on policy will likely evolve with them.”

Communicating those intentions clearly without roiling the markets has proved challenging for the once-secretive institution. On Wednesday, Yellen suggested that the first rate hike could come “something on the order of around six months” after the Fed stops pumping money into the economy through its bond-buying program this fall. She qualified that, saying the decision will be dependent on economic data, but Wall Street seized on the time frame as a suggestion that the move will come earlier than expected. The major indexes ended the day down more than half a percentage point.

Officials will try “to provide as much clarity as is reasonably certain, given that the economic developments in the economy are themselves uncertain,” Yellen said Wednesday. “But we will try as hard as we can not to be a source of instability here.”

The Fed sets the target for what is known as the federal funds rate, which determines how much banks can charge to lend to each other overnight. That rate influences the pricing of a broad array of business and consumer loans, including mortgages and car notes.

The central bank began cutting that interest rate in the fall of 2007 amid emerging signs of the financial turmoil that would usher in the worst economic downturn in the United States since the Great Depression. It continued to slash rates over the next year — the financial equivalent of flooring the gas pedal in hopes of keeping the economy from wrecking. In December 2008, the federal funds rate hit zero.

But the Fed struggled to convince wary investors that it had no intention of letting its foot off the accelerator anytime soon. To reassure markets, the central bank made a series of increasingly definitive promises that it would leave interest rates untouched. Most recently, it vowed not to raise rates at least until the unemployment rate hit 6.5 percent.

Now, the economy is approaching that threshold. The unemployment rate was 6.7 percent in February. but there remains little agreement over how fast the Fed may need to act once that milestone is met.

The unemployment rate has fallen faster than officials expected as workers retire or leave the labor force discouraged. Some officials believe the Fed should keep interest rates low until the economy is close to full employment — or even beyond that point — in an effort to recapture those lost workers. Others argue that keeping rates low for too long risks stoking inflation and financial instability.

On Wednesday, Yellen indicated that the low level of inflation gives the Fed plenty of room to maneuver. Even after the first rate hike, Fed officials could decide to keep interest rates below their normal level of 4 percent for some time.

“The committee, today, for the first time, endorsed that” in its official statement, Yellen said.

But a survey of Fed officials released Wednesday suggests that future increases could come more rapidly. Four officials think rates could be at 1 percent at the end of 2015, two more than in December. By the end of 2016, a growing number of officials believe, rates could be 2 percent or higher. Yellen called those moves a “very limited upward drift.”

Fed officials also slightly lowered their forecasts for economic growth to 2.8 to 3 percent this year and 3 to 3.2 percent next year. However, they predicted the unemployment rate will fall more quickly, reaching 6.1 to 6.3 percent this year and 5.6 to 5.9 percent in 2015. There was little change in the inflation forecast.

The Fed’s policy-setting committee approved the statement 8 to 1. Minneapolis Fed President Narayana Kocherlakota dissented over concerns that the statement did not emphasize the Fed’s commitment to meeting its 2 percent target for inflation. He has advocated for a more definitive promise not to raise rates until the jobless rate hits 5.5 percent.

But Yellen said Wednesday that the Fed believes inflation will slowly but surely rise.

“We do not want to undershoot inflation for a prolonged period of time,” she said, adding, “If the committee had real concerns that inflation were going to remain persistently below 2 percent, I feel confident that the committee would act to prevent that.”

In addition, the Fed voted to continue reducing the amount of money it is pumping into the economy. The Fed has been buying bonds to help push down long-term interest rates and boost demand from consumers and businesses. Over its past two meetings. the Fed scaled back those purchases by $20 billion to $65 billion. It will cut the amount to $55 billion.