US gross domestic product expanded at a 2.6 per cent annual rate in the October-December period.

The result, released by government on Thursday, was down from a 3.4 per cent rate in the July-September period and a sizzling 4.2 per cent pace from April through June.

During those months, the economy benefited from tax cuts and from higher government spending, the gains from which are thought to be fading.

Read Next For 2018 as a whole, US GDP growth amounted to 2.9 per cent, the government said, the best showing since 2015.

It was just below the 3 per cent pace the administration has said it can maintain consistently.

By contrast, most economists foresee slower growth ahead. For the current January-March quarter, many analysts say they think growth could slow to a 2 per cent annual rate or less.

"I think the economy will be steadily throttling back over the next two years," said Mark Zandi, chief economist at Moody's Analytics.

The economy's pace of expansion last quarter reflected a slowdown in consumer spending and the start of a 35-day partial shutdown of the government, which subtracted an estimated 0.1 percentage point from growth.

That weakness was offset somewhat by a gain in business investment and less of a drag from trade.

The $US1.5 ($A2.1) trillion tax cut President Donald Trump pushed through Congress in late 2017 and billions of extra dollars in government spending Congress added for military and domestic programs helped accelerate the economy last year.

In the view of most economists, though, 2018 may turn out to have been the economy's high point for some time.

Many are forecasting that growth this year will slow to around 2.2 per cent and to weaken further in 2020.

Some analysts say they think the economy could even dip into recession next year as the support from the tax cuts fades and the global economy sputters.