By Jon Hilsenrath And Jeffrey Sparshott 

The economy's sharp first-quarter slowdown is giving Federal Reserve officials pause.

The nation's central bank pointed to cooling economic activity and reduced job-market gains in its policy statement Wednesday, underscoring uncertainty among officials about when the economy will rebound and clouding the timing of when they will begin to raise interest rates. Earlier in 2015, many officials thought a midyear rate increase was possible. Now it looks highly unlikely.

"Economic growth slowed during the winter months, in part reflecting transitory factors," the Fed said. "The pace of job gains moderated, and the unemployment rate remained steady."

The Fed's two-day policy meeting concluded a few hours after the Commerce Department reported that gross domestic product, the broadest measure of economic output, grew at a 0.2% annual rate in the first quarter. That followed advances of 2.2% in the fourth quarter and 5% in the third.

Fed officials sought to look beyond another winter economic disappointment by noting that household incomes and confidence were rising and growth was expected to return to a modest pace.

Still, they want firm evidence the economy is stronger before they start lifting their benchmark short-term interest rate, which has been near zero since December 2008.

Bad weather, cheaper oil, disruptions at West Coast ports and the stronger dollar appear to be at least partly behind the downturn. In the first three months of the year, consumers showed signs of caution about spending, businesses slashed investment--especially in the energy sector--and exports tumbled, marking a return to uneven growth that has been a hallmark of the nearly six-year economic expansion.

The port shutdowns and cold winter are over, so many economists expect growth to pick up. But cautious consumers, an investment bust in oil-producing states and a strong dollar's hit to exports could be longer-lasting impediments to a big rebound.

A stronger dollar has made domestically produced goods more expensive overseas and foreign products cheaper inside the U.S. A widening trade gap has subtracted from economic output in four of the past five quarters, according to the Commerce Department.

"It's hard to sugarcoat today's number--it was disappointingly soft," Michael Feroli, chief U.S. economist at J.P. Morgan Chase, said of first-quarter growth in GDP.

Wednesday's economic news has become an all-too-familiar pattern. The economy seems to repeatedly stumble in the dreary winter months. Statistical procedures used by government number-crunchers are meant to smooth out seasonal swings in the economy, such as slowdowns in home building during winter months or hiring and layoffs of retail workers around Christmas.

Still, the sluggishness in winter growth readings persists. Last year, economists pinned much of the blame for a bad first quarter--GDP fell at a 2.1% annual rate--on unusually harsh weather. This year, the Northeast was again hit with blizzards that may have briefly muted consumer spending and business activity.

Since 2010, first-quarter GDP growth has averaged 0.6% while all other quarters 2.9%. That stop-and-start pattern has forced Fed officials to regularly second-guess their own economic forecasts.

Fed officials now need time to ensure their expectation of a rebound proves correct.

Officials in March opened the door to rate increases later this year by removing from the policy statement assurances that they would stay patient on timing. But they said they won't move until they become reasonably confident that inflation is rising toward the Fed's 2% objective and as long as the job market continues to improve.

The fact that the job market didn't improve since the last meeting means Fed officials are in no hurry to move. Many analysts are now looking toward a move in September or later in the year, rather than June.

"You would have to see a pretty significant surprise on the upside [for the economy] to put June back on the table," said Tim Hopper, chief economist at TIAA-CREF, the retirement fund manager.

While the Fed looks for evidence the economy has regained its footing, the oil patch is hurting.

Wilco Machine & Fab Inc., a Marlow, Okla., maker of storage tanks, portable silos, tools and other specialty equipment used largely in the oil and gas industry, expects its sales to drop by 50% this year and also has cut its employment in half at its plant.

"I see this as a very tough and challenging year with many hard decisions to make," said company President Brad Boles. "We will get through this downturn, but not without losing many good employees and suppliers."

Mr. Boles said oil prices will have to rise back to about $75 a barrel before customers to start ordering new equipment. Crude-oil prices have come off of recent lows but on Wednesday remained below $60 a barrel.

Across the nation, nonresidential fixed investment--which reflects spending on software, research and development, equipment and structures--fell at a 3.4% rate in the first quarter, compared with a 4.7% increase in the fourth quarter. Business investment in structures dropped at a 23.1% rate, led by a 48.7% contraction for mining sector spending on shafts and wells, Commerce said.

Much of what businesses produced ended up in stockpiles. Rising inventories contributed 0.74 percentage point to GDP in the first quarter. In the second quarter, producers are more likely to allow inventories to run down rather than building them up even more, which would be a new drag on growth.

Still, the outlook has some clearer bright spots. The finances of American households are improving, thanks to job gains and the benefits of cheaper gas. After-tax incomes adjusted for inflation were up at an annual rate of 6.2% from the prior quarter, the biggest gain since late 2012.

The Fed pointed to gains in household income as evidence of underlying economic vigor.

Still, the GDP report showed that consumer spending grew at a 1.9% pace in the first quarter, down from 4.4% in the fourth quarter. Rather than using savings from cheaper gasoline to buy more goods and services, Americans have been setting money aside for a rainy day. The personal saving rate at 5.5% in the first quarter was the highest since 2012. The figure was 4.6% in the fourth quarter. Money not spent now might be spent later.

Some companies have been caught in multiple economic crosscurrents.

Sales at C.R. Onsrud Inc. slowed in the first quarter. "We weren't losing any business, but it seemed like everyone was delaying projects," said Andy Turner, regional sales manager at the Troutman, N.C., maker of precision routers and other computer-assisted machines.

Clients in the Northeast weren't working because of severe weather and told Mr. Turner to hold off on visits. And some furniture and cabinet companies, which use Onsrud's machines to cut wood, were slow to get raw materials while they piled up at West Coast ports. "They didn't want to buy machines because they didn't have anything to put on them," he said.

But so far April has been the busiest month of the year and Mr. Turner expects 2015 sales to grow slightly from last year, when revenues hit about $36 million.

One obstacle has been a stronger dollar. Exports account for only about 5% of sales at Onsrud, which makes machines that sell for around $200,000 each. But the company competes against European and Asian manufacturers with similar products.

"The reality is that in some cases we have to work off of a slimmer [profit] margin to get the same business that we would have been able to get when the dollar was weaker," Mr. Turner said. "It's hurting us here in the U.S. All of the machines that are being imported now basically got a big price cut."

Write to Jeffrey Sparshott at jeffrey.sparshott@wsj.com and Jon Hilsenrath at jon.hilsenrath@wsj.com