WASHINGTON (MarketWatch) — The U.S. economy grew 3% in the fourth quarter, faster than originally reported, mainly because of increased commercial construction, higher consumer spending and lower imports, the government said Wednesday.

The Commerce Department initially estimated the U.S. expanded at a 2.8% pace in the final three months of 2011. It’s still the fastest rate of growth in a year and a half.

Economists surveyed by MarketWatch had predicted GDP growth would be revised down to 2.7% from an initial reading of 2.8%.

Much of the fourth quarter’s growth stemmed from an unexpectedly large buildup in inventories. The government trimmed its initial estimate of a $56 billion increase in inventories to $54.3 billion.

Economists expect companies to cut back on inventories in the first three months of 2012. As a result, growth is expected to slow to 1.9% in the first quarter, the latest MarketWatch forecast shows.

In the revised fourth-quarter report, meanwhile, the government raised its estimates for commercial construction and consumer spending.

Investment in nonresidential structures, a major category of business investment, climbed 2.8% in the fourth quarter instead of 1.7% as originally reported.

Consumer spending rose 2.1% on an inflation-adjusted basis compared to an earlier reading of 2.0%. Even a small change can be big since consumers account for as much as 70% of U.S. economic growth.

Real final sales in the U.S., which excludes imports, increased 1.1% vs. an initial calculation of 0.9%. This category is viewed as the best indicator of economic activity in the GDP report because it measures domestic consumer demand.

Purchases of durable goods such as automobiles jumped 15.3% in the fourth quarter, compared to an earlier estimate of 14.8%. That was about three times faster than in the third quarter.

Investment in homes and apartments was also revised up to an 11.5% increase.

Imports, which subtract from GDP, did not rise as much as initially believed. The government said imports rose 3.8% in the fourth quarter, down from a prior estimate of 4.4%.

Exports rose 4.3%, smaller than then original reading of 4.7%

Spending by governments at all levels fell a combined 4.4% in the fourth quarter instead of 4.6% as initially projected. Lower government spending was one of the biggest drags on growth in the final months of the year.

Inflation as measured by the consumer PCE index rose 1.2% in the fourth quarter, or by 1.3% on a “core” basis if food and energy are excluded.

Real disposable income climbed 1.4% in the fourth quarter, compared with an earlier reading of 0.8%. The personal savings rate was 4.5%, up from an initial estimate of 3.7%.