monthly reductions in Treasury holdings of no more than $6 billion and $4 billion in mortgage bonds. Those figures would rise in increments over a year until they reached $30 billion a month in Treasurys and $20 billion in mortgage bonds.

“With the Fed stating its intentions to start reducing the size of the balance sheet this year, it is offering a clear vote of confidence for the economy,” said Curt Long, chief economist of the National Association of Federally Insured Credit Unions.

Chair Janet Yellen was asked at a news conference whether she worried that the Fed could rattle markets once it starts shrinking its bond holdings. She said the central bank feels confident it can avoid “market strains” by detailing its plan far in advance and by stressing that the process will be gradual.

The Fed provided no date for the start of the bond sales but said that if the economy fares as expected, “we could put this into effect relatively soon.”

The Fed also issued updated economic forecasts that showed it foresees one additional rate increase this year to follow Wednesday’s increase and an earlier rate hike in March.

The rate forecast, based on individual projections from each member, envisions three more rate hikes in 2018 and three more in 2019. By then, the Fed’s forecast would put its key policy rate at 3 percent. That’s the level the Fed believes is a neutral rate — neither stimulating growth nor restraining it.

But the Fed’s forecasts are only predictions and are frequently revised as its assessments evolve. Some economists suggested that even though the Fed foresees one more rate hike this year, the persistently low inflation may lead it to leave rates alone until 2018. Some also note that political paralysis in Washington has raised doubts about whether Congress will increase the nation’s borrowing limit and pass a new budget. That possibility, too, could lead the Fed to wait.

Another rate hike this year is “becoming less of a sure thing as every month of data comes out,” said Michael Dolega, senior economist at TD Economics. If inflation doesn’t pick up, he said, the Fed will find that raising rates and reducing its balance sheet is “going to be a difficult maneuver.”

The Fed’s revised forecasts reduced its estimate for unemployment by year’s end to 4.3 percent from a March projection of 4.5 percent. Unemployment has already reached a 16-year low of 4.3 percent.

The Fed kept forecast for economic growth this year of 2.2 percent, up slightly from its March forecast, with growth of 2.1 percent in 2018 and 1.9 percent in 2019. Those forecasts are far below the 3 percent annual growth the Trump administration has said it can achieve.

President Donald Trump is expected soon to fill three vacancies on the Fed’s influential board, and those new members, depending on who they are, could alter its rate-setting policy.

The betting is that the administration will choose officials who will tilt the Fed toward a more “hawkish” stance.

Yellen, the first woman to lead the Fed, is serving a term that will end in February. So far, Trump has sent conflicting signals about whether he plans to nominate her for a second term.