Facing a rising citywide demand for electricity, a Brooklyn-based power plant is seeking to increase its capacity, with plans to spend more than $100 million to expand its Sunset Park facility.

The owner of the plant, Astoria Generating Company, a subsidiary of US Power Generating Company, announced yesterday that it is applying to add 100 to 150 megawatts of capacity to its 560-megawatt facility, an alteration that will require the operator to go through a lengthy environmental review process.

In a statement, the company pledged that the changes to its facility would result in a net decrease in emissions, a commitment that received praise from Mayor Bloomberg.

“It could serve as a prime example of an innovative measure that promotes both environmental sustainability and economic development,” Mr. Bloomberg said in a statement.

The city has been pushing for power companies to invest in cleaner energy as the city’s demand for electricity increases with its population. The Bloomberg administration’s long-term sustainability plan, PlaNYC, predicts total demand for electricity will grow by 44% between 2005 and 2030, rising to 72 million megawatts a year.

The announcement by US Power Generating Company was greeted with caution by a community group critical of the Sunset Park plant, Uprose.

“If the proposal itself can demonstrate that there will be a net reduction, then that’s something that we will live with,” the group’s executive director, Elizabeth Yeampierre, said of emissions. “We understand that there is an increased demand for energy.”