WASHINGTON — The economic expectations of leading U.S. chief executives have dropped to the lowest level in three years amid concerns about taxes and the global economy, according to survey results released Tuesday.

Reduced expectations for sales and capital spending over the next six months pushed down the quarterly economic outlook index from the Business Roundtable, a trade association of CEOs of the largest U.S. corporations.

It was the third straight decline for the index, which fell to 67.5 in the fourth quarter from 74.1 in the previous quarter.

The index’s long-term average is 80.1 within its range of 150 to negative 50. It dropped to negative 0.5 at its low during the Great Recession and has reached as high as 113 during the recovery.

“Lower expectations for sales and investment reflect CEOs’ ongoing caution about the near-term prospects for U.S. economic growth,” said AT&T Inc. Chief Executive Randall Stephenson, the group’s chairman.

Still, short-term hiring plans held steady in this quarter’s survey, with 35 percent of respondents expecting to increase their company’s workforce.

The more pessimistic overall outlook was caused by several factors, Stephenson said.

The Paris terrorist attacks could make consumers and businesses more cautious. And exports have been hurt by the slowing global economy and strong U.S. dollar, he said.

Meanwhile, CEOs are concerned that Congress has yet to extend some key expiring tax provisions, while broader efforts to overhaul the corporate tax code appear stalled.

The U.S. has the highest corporate tax rate of the major developed countries that make up the Organization for Economic Development and Cooperation.