WASHINGTON (AFP) - US consumers grew slightly more confident in August as they viewed economic conditions and job prospects improving in the future, the Conference Board said on Tuesday.

The consumer confidence index rose to 81.5 last month, up from 81.0 in July but still below the five-year high of 82.1 reached in June.

The improvement in confidence, a partial predictor of consumer spending that drives the economy, surprised analysts, who generally had forecast the index would drop to 77.0.

But the overall stronger sentiment number was entirely due to expectations for conditions six months ahead; the reading jumped to 88.7 from 86.0 in July.

Consumers' views of current conditions deteriorated to 70.7 from 73.6 last month.

"Consumers were moderately more upbeat about business, job and earning prospects," Ms Lynn Franco, director of economic indicators at the Conference Board.

She noted that income expectations, which had fallen after the January payroll tax hike, rebounded to their highest level in two and a half years.

Higher incomes could boost consumer spending, which accounts for about two-thirds of US economic activity.

"This report is consistent with our expectation that consumer confidence will continue to grind higher as labour and housing markets continue to improve," said Cooper Howes of Barclays.