* Delta to replace 50-seater jets with CRJ900
* Firm orders for 40 jets valued at $1.85 bln
* Shares of rival Embraer fall
Dec 6 (Reuters) - Bombardier Inc said Delta Air Lines Inc placed firm orders for 40 NextGen jets, with the option to buy another 30, in a deal valued at up to $3.29 billion.
Delta, the U.S. No.2 airline, said the purchase is part of its domestic fleet restructuring to replace less efficient, small aircraft with bigger jets.
The firm orders were valued at $1.85 billion, Bombardier said.
Shares of rival Brazilian aircraft maker Embraer SA fell 7 percent - their biggest intraday loss in nearly five months - following the news.
Bombardier last month won its biggest jet deal of $7.8 billion from Swiss charter operator VistaJet for up to 142 Global aircraft.
The Canadian aircraft and train maker's stock is trading at about 8 times analysts' expectations for 2012 earnings, according to Thomson Reuters data.
Rival Boeing is at about 15 times forward earnings.
The new Bombardier CRJ900 NextGen regional jets would be configured with 76 seats in a two-class cabin and will replace Delta's 50-seater jets. Delta already has 101 CRJ900 aircraft.
The company previously said it would add 88 Boeing 717-200 aircraft and acquire 100 Boeing 737-900ER jets.
Delta said on Thursday that it expects all of the aircraft to be delivered in the latter half of 2013.
Shares of Montreal-based Bombardier were up 3.7 percent at C$3.40 on the Toronto Stock Exchange on Thursday, while Delta was up 1 percent at $9.81 on the New York Stock Exchange.