DUBAI, Oct 17 (Reuters) - Saudi Hollandi Bank 1040.SE , Saudi Arabia's oldest lender, posted a 46.7 percent fall in third-quarter net profit on Monday, widely missing analysts forecasts as it was forced to set aside cash to cover an increase in bad loans.

The lender made a profit of 262.8 million riyals ($70.1 million) in the three months to Sept. 30, down from 493.0 million riyals in the corresponding quarter of 2015, according to a bourse filing.

Three analysts polled by Reuters had forecast on average Saudi Hollandi would make a quarterly profit of 506.4 million riyals.

The bank cited a 67.6 percent rise in total operating expenses for the lower earnings, mainly due to an increase in impairment charges.

This offset a 3.6 percent increase in total operating income to 911.2 million riyals, which was boosted by a 9.6 percent gain in profit from special commissions to 664.1 million riyals.

Saudi banks are struggling as cheap oil cuts state revenues and forces the government into expenditure cuts, weighing on consumer spending and business activity, while pushing up bad loans.

The bank's loans portfolio stood at 77.26 billion riyals at the end of September, 5.1 percent higher than the same point of 2015, according to the statement, while its deposit base gained 1.5 percent year on year to 84.2 billion riyals.

($1 = 3.7495 riyals)

(Reporting by Tom Arnold; Editing by David French) ((Tom.Arnold@thomsonreuters.com; +97144536265; Reuters Messaging: tom.arnold.thomsonreuters.com@reuters.net))