BOSTON (Reuters) - Billionaire investor William Ackman is playing an outsized role in railway Canadian Pacific's (>> Canadian Pacific Railway Limited) plan to buy rival Norfolk Southern (>> Norfolk Southern Corp.), underscoring his efforts to bring home a deal to salvage an otherwise awful 2015 for the hedge fund manager.

Ackman sits on Canadian Pacific's board of directors and his $14.8 billion Pershing Square Capital Management owns 9.1 percent of the company. Ackman was the last to speak on a conference call on Tuesday that spelled out an enhanced bid for Norfolk Southern.

By the time the call ended 2-1/2 hours later, Ackman was doing most of the talking, laying out how much Norfolk Southern shareholders could earn on a merger, noting that Canadian Pacific would be willing to agree to a breakup fee if a deal did not materialize, and highlighting what he called a lack of operational expertise by Norfolk Southern's chief executive, James Squires.

Ackman became a favorite with pension funds and wealthy investors by delivering double-digit returns since launching his firm. This year, however, he is down 17 percent, mainly because his bet on drugmaker Valeant Pharmaceuticals (>> Valeant Pharmaceuticals Intl Inc) has crumbled - and in contrast to last year's 40 percent gain.

At CP, Ackman had not participated in a company conference call since Pershing Square's 2012 landslide proxy victory which earned him and partner Paul Hilal board seats and allowed him to hand-pick CP CEO Hunter Harrison.

Pershing Square has quadrupled its money on its investment in Canadian Pacific since 2011. But Ackman's bet on the company has been under pressure as railroad stocks have pulled back roughly 30 percent this year amid slower growth in China.

Investors in Pershing Square say a deal that would boost CP's stock could help the hedge fund narrow its loss this year.

Ackman underscored that Harrison made overtures to CSX Corp (>> CSX Corporation) last year and said Harrison is driving the bid to buy Norfolk Southern this year. On the call Ackman and Harrison said they have both been in touch with Norfolk Southern shareholders who want their help in improving the company's performance.

Ackman has used his position as an investor to push for deals before. Last year he worked with Valeant on its failed bid to buy Allergan.

(Reporting by Svea Herbst-Bayliss; Editing by Joe White and Leslie Adler)

By Svea Herbst-Bayliss