After initially saying output increased at an annual rate of 2 percent, the Commerce Department on Thursday revised its estimate to show growth of 2.7 percent in the three months that ended Sept. 30.

    While businesses have remained cautious amid fiscal uncertainty in Washington and weak growth overseas, consumer spending in the United States has moved along in recent months at a healthier pace.

     In addition, a strengthening housing market in many regions, along with better employment figures, has reassured some analysts who feared the economy was close to stalling.

     However, worries remain about growth in the current quarter, with many economists estimating output to increase at a more tepid rate of roughly 1 percent.

    And with more than $600 billion in tax increases and spending cuts looming if Congress and the White House can’t agree on a deal to cut the deficit by Jan. 1, economists warn the economy remains vulnerable.

    The newly estimated pace of growth represents a substantial increase in the level of expansion from the second quarter, when the economy grew at a rate of just 1.3 percent. It also marks the fastest rate of expansion since the fourth quarter of 2011, when the economy grew at a 4.1 percent pace.

This was the second of the government’s three estimates of quarterly growth. The final figure is scheduled for Dec. 20.