(Corrects value of deal to $4.17 billion from $9.5 billion, deletes reference to no premium in 3rd paragraph)
* All-stock deal
* Combined co would have 3.5 mln gas, power customers
* Shareholders vote seen in early 2011
NEW YORK, Oct 18 (Reuters) - Northeast Utilities NU.N will buy peer NSTAR NST.N in a $4.17 billion all-stock deal to create one of the largest U.S. utilities, the companies said on Monday.
The deal calls for the exchange of 1.312 common shares of Northeast Utilities for each NSTAR share.
That ratio was based the average closing price of both companies' shares over the past 20 trading days, the companies said.
Upon completion, Northeast Utilities would operate six regulated electric and gas utilities in three states with nearly 3.5 million electric and gas customers.
The companies said they expected the merger to produce "important long term net savings as a result of efficiencies," and the combined entity would spend $9 billion on the region's energy infrastructure over the next five years.
The companies expect to seek the necessary two-thirds approval from shareholders in early 2011, if the deal is approved by state and federal regulators. (Reporting by Matt Daily; Editing by Lisa Von Ahn)