By Blaise Robinson and Benjamin Mallet

PARIS (Reuters) - Alstom (ALSO.PA: Quote, Profile, Research) posted a bigger than expected 56 percent rise in full-year net profit and boosted its medium-term outlook on Wednesday, as the maker of power plants and fast trains reaped the benefit of high orders.

The company, which will double its dividend to 1.6 euros per share, said that given its strong backlog, the operating margin in March 2010 should exceed its previous forecast and reach around 9 percent.

Alstom Chief Executive Patrick Kron told a conference call that he saw Alstom's 2008-2009 operating margin between 7.7 percent and 9 percent.

The French engineering firm reported net profit of 852 million euros ($1.32 billion) in the year ended March 31, while income from operations rose 35 percent to 1.295 billion euros, generating a margin of 7.7 percent, compared with 6.7 percent the year before.

Analysts had forecast net profit of 812 million euros, according to Reuters Estimates.

Free cash flow jumped 119 percent to a record 1,635 million euros, making the company strongly cash positive as at March 2008, Alstom said.

Alstom shares were up 2 percent at 152.40 euros, among the top gainers on France's benchmark CAC-40 index .FCHI.

"Alstom has produced another set of excellent results, beating numbers, setting records and raising guidance for the period to March 2010. The record cashflow and the move to a net cash position has allowed the company to double last year's dividend," said Stephen Surpless, senior analyst at Cantor Fitzgerald.