U.S. chief executive officers are gloomier about their plans for hiring and capital expenditures over the next six months, and are more wary about their sales prospects, according to a quarterly survey from the Business Roundtable released on Tuesday.

The CEOs' hiring plans were particularly weaker, with 34 percent expecting employment to increase in the next six months, down from 43 percent in the Business Roundtable's second-quarter survey.

The chief executives expect U.S. gross domestic product growth of 2.4 percent this year, compared to their estimate of 2.3 percent growth in the second-quarter survey.

"While some U.S. economic indicators are improving moderately, the results from our survey of CEOs seem to reflect an underperforming U.S. economy held back by policy uncertainty and growing conflicts around the world," Randall Stephenson, chairman of Business Roundtable and CEO of AT&T Inc (T.N), said in a release.

The Business Roundtable CEO Economic Outlook Index, a composite index of expectations for sales, capital spending and employment over the next six months, fell in the third quarter to 86.4 from 95.4 in the second quarter. An index above 50 indicates an economic expansion.

(Reporting by Lewis Krauskopf; Editing by Meredith Mazzilli)