* Organic brokerage revenue declines 3 pct

* Total revenue down 2 pct; expenses flat

* Future growth could come from acquisitions

* Shares fall nearly 6 percent (Recasts; adds analyst comment, CEO and CFO comments, byline; updates share move)

By Lilla Zuill

NEW YORK, Oct 30 (Reuters) - Aon Corp AOC.N, the world's largest insurance brokerage, said its brokerage unit's organic revenue growth declined for the first time in 16 quarters, sending its shares down nearly 6 percent.

The news overshadowed Aon's report of slightly higher third-quarter profit, with operating earnings about in line with expectations.

"The key takeaway in the quarter was disappointing revenue" for the brokerage unit, Citigroup analyst Keith Walsh wrote in a research note.

Walsh said while insurance brokers have been plagued recently by declining revenue, he had expected Aon to buck the trend. He said the drop-off in revenue from reinsurance brokerage and in the Americas had been especially disappointing.