UPDATE 3-Exelon to abandon NRG bid if no directors elected

* Exelon will walk away if none of its directors elected

* Will press forward if all nine elected (Updates share price)

NEW YORK, July 15 (Reuters) - Exelon Corp (EXC.N) on Wednesday said it will pull its hostile bid for NRG Energy Inc (NRG.N) if none of the slate of directors it has put up for election to NRG's board are voted in.

NRG shares fell more than 2 percent after the announcement.

"If this is the outcome of the vote, the desires of NRG stockholders will be clear. We will abandon our efforts to acquire NRG and go our own way," Exelon Chief Executive John Rowe said in a letter to NRG's shareholders.

Exelon, the largest U.S. nuclear power company, is currently bidding 0.545 of its shares -- or around $28.10 on Wednesday afternoon -- for every NRG share.

NRG, whose shares are currently trading at $24.74, has rejected that offer as too low.

As part of its hostile offer, Exelon has proposed to expand NRG's board to 19 seats from 14 and elect nine new directors.

Exelon said if all nine of its directors are elected, it "will press forward with determination" in its bid, but will remain disciplined with respect to price.

If only four new directors are elected, the company said it may or may not proceed with the bid.

The four top proxy advisory firms have recommended shareholders reject Exelon's proposals at NRG's annual meeting, which is to be held on July 21.

RiskMetrics, the top proxy adviser, has suggested shareholders would support a deal if Exelon raised its bid to around 0.6 of its shares for every NRG share.

Exelon, the largest U.S. nuclear power company, made its initial hostile bid for the independent power producer in October and raised its bid earlier this month.

NRG declined to comment on the letter. The company's shares were down 11 cents at $24.74 in late afternoon trading, while Exelon shares were up $1.51, or 3 percent at $51.59. (Reporting by Michael Erman; Editing by Phil Berlowitz)