--HidroAysen will submit its transmission-line environmental study at the end of this year

--The study will cover 850km, including 160km underwater

--HidroAysen's delay fuels concerns over project's start-up date as energy supply could become a chronic issue in long run

(Adds information regarding the environmental transmission line study from the fifth paragraph)

By Graciela Ibanez

Of Dow Jones NEWSWIRES

SANTIAGO (Dow Jones) -- Chile's giant HidroAysen power project once again delayed the environmental impact study for its nearly 2,000-kilometer transmission line.

The controversial $3 billion, 2,750-megawatt HidroAysen project, which is being developed as a joint venture by power generators Empresa Nacional de Electricidad SA (EOC, ENDESA.SN) and Colbun SA (COLBUN.SN), received a legal green light earlier in April as Chile's Supreme Court rejected an appeal from regional and environmental organizations to stop construction of its generation units.

The project's next step, before starting the units' construction, is obtaining approval for its $4 billion transmission line.

HidroAysen will submit the line's environmental study for authorities' approval at the end of this year, the project's chief executive, Daniel Fernandez, told Dow Jones Newswires.

In light of the government's announcement it will build an "electric highway", or transmission backbone, from the southern city of Puerto Montt to northern Chile, HidroAysen's study will cover a line of about 850 kilometers, 160 km of which is underwater, which will go from Puerto Montt further south to the city of Cochrane, Fernandez added.

HidroAysen was first expected to hand in the study last December, but it delayed the study to March and then again to June of this year, fueling concerns over the start-up date.

The transmission-line study's submission date has been delayed as HidroAysen wants to hand in a more complete study that will include a second round of interviews with the inhabitants of the area where the line will go through, said a person close to HidroAysen.

Chile needs to nearly double its current installed capacity of 15,000 megawatts over the next decade to keep up with rising demand. Otherwise, the country's energy supply will be jeopardized in the long run.

Legal battles over the construction of HidroAysen plants have already delayed the start-up for a year.

HidroAysen has faced staunch opposition because of its plans to build the transmission line through vast expanses in Patagonia and also to dam the Baker and Pascua rivers to feed five generation plants.

-By Graciela Ibanez, Dow Jones Newswires; 56-2-715-8929; graciela.ibanez@dowjones.com