WARWICK, R.I. – Rhode Island regulators Tuesday dealt a major setback to a proposed offshore wind farm, rejecting an agreement between Deepwater Wind and National Grid, a major electric utility.

The Public Utilities Commission voted unanimously Tuesday to reject a proposed agreement by Deepwater Wind to sell power from eight turbines proposed off Block Island.

Gov. Don Carcieri, who has said the wind farm and power-purchase agreement would create jobs and benefit the environment, said he was “stunned” and disappointed by a decision that he called narrow-minded. He said he would discuss alternatives with legislative leaders.

Hoboken, N.J.-based Deepwater Wind said it would rethink its commitment to Rhode Island.

“This vote is a serious setback to Rhode Island’s plans to become the leader in the nation’s offshore wind industry,” the firm said in a written statement.

The Block Island plan was to have been a demonstration for what Deepwater Wind hoped would eventually be a larger offshore project involving about 100 turbines.

A 20-year purchase agreement signed last December called for National Grid to pay Deepwater Wind 24.4 cents per kilowatt hour of electricity starting in 2013.

“While the price for the power from this Block Island demonstration project is higher than current electricity rates, I, along with many others, feel that over 20 years this differential is likely to disappear,” the Republican governor said in a statement.

The environmental group Conservation Law Foundation said it was disappointed by the PUC’s ruling.