* Deal to value Ansaldo Energia above 1 bln euros - source
* Finmeccanica shares up 1.7 percent, outperform market
(Adds details, share price)
ROME, March 4 (Reuters) - Italy's Finmeccanica is set to sell 45 percent of wholly owned unit Ansaldo Energia to U.S. fund First Reserve, a source close to the matter said on Friday.
The deal values Ansaldo Energia, which produces thermoelectric power plants, at just above 1 billion euros ($1.4 billion), the source told Reuters.
Finmeccanica will call an extraordinary board meeting shortly to approve the sale, the source said.
The Italian aerospace and defence group had been in talks with the U.S fund for some months after negotiations with a Japanese group fell apart.
The deal will be carried by setting up a vehicle company, in which Finmeccanica will have 55 percent and First Reserve the remainder.
Finmeccanica shares were up 1.7 percent at 9.015 euros by 1021 GMT, outperforming the 1.1 percent gain in the Milan blue- chip index.
($1=.7170 EURO)
(Reporting by Paolo Biondi; Editing by Erica Billingham)