By Joshua Franklin and Greg Roumeliotis

June 30 (Reuters) - Investment firm Brookfield Asset Management Inc has agreed to acquire U.S. freight railroad owner and operator Genesee & Wyoming Inc for close to $9 billion, including debt, people familiar with the matter said on Sunday.

Genesee & Wyoming's decision to sell itself comes after its string of acquisitions of short-line railroads made investing in the maintenance of its expanding network more expensive, amid weakness in some of its core North American markets for the transport of steam coal and agricultural products.

Some buyout firms such as Brookfield specialize in helping companies they buy bankroll further acquisitions to consolidate their sectors. The deal shows Brookfield is not fazed by the uncertainty that the trade war between the United States and China has cast on Genesee & Wyoming's business.

A Brookfield infrastructure fund has agreed to pay more than $110 per share in cash for Genesee & Wyoming, the sources said, requesting anonymity ahead of an official announcement expected as early as Monday. Genesee & Wyoming shares ended trading on Friday at $100.

Toronto-based Brookfield declined to comment, while Genesee & Wyoming did not immediately respond to a request for comment.

Based in Darien, Connecticut, Genesee & Wyoming owns or leases 120 freight railroads in the United States, Canada, Britain and continental Europe.

The company's revenues have increased at a compound annual growth rate of 16.8% since it floated in the stock market in 1996, rising to $2.3 billion in 2018 from $77.8 million, according to Genesee & Wyoming's latest annual report.

Much of that growth was fueled by Genesee & Wyoming's acquisition of short-line rail assets from "Class I" carriers in North America, the biggest operators focusing on longer routes. The transport of many commodities relies on the short-line rail roads that Genesee & Wyoming operates.

"Medium-term growth opportunities (for Genesee & Wyoming) remain solid, including a healthy North American pipeline of industrial development projects and spot-coal haulage contracts in Australia," Morningstar analysts wrote in a research note last month.

The acquisition of Genesee & Wyoming would be the latest big leveraged buyout by Brookfield, which agreed last year to buy Johnson Controls International Plc's power solutions business for about $13 billion.

Bloomberg News reported last week that an affiliate of Brookfield was "the frontrunner" to acquire Genesee & Wyoming following an auction for the company. (Reporting by Joshua Franklin and Greg Roumeliotis in New York; Editing by Peter Cooney)