A Colorado-based electricity supplier for 1.4 million customers in four states is reviewing its plans for coal-based power, as a dispute over a proposed plant in Kansas drags on.

The Tri-State Generation and Transmission Association board said Friday it is re-evaluating all long-term plans from 2005 for resources, whether for fossil fuels or renewable energy.

Under the 2005 plan, Tri-State hoped to buy power from two coal-fired plants that Sunflower Electric Power Corp. proposed building in Kansas.

But in 2007, Kansas Department of Health and Environment Secretary Rod Bremby blocked Sunflower’s proposal over concerns about potential carbon dioxide emissions and global warming. Sunflower is seeking legislative relief to build the plants, but it may not survive a veto.

Tri-State general manager Ken Anderson said that keeps the Kansas project out of the near-term picture. Long-term prospects are unclear. In the meantime, Tri-State is expanding energy-efficiency programs, investing in renewable energy and increasing natural gas capacity.

Tri-State is based in the Denver suburb of Westminster, and its member cooperatives serve consumers in Colorado, Nebraska, New Mexico and Wyoming.

Tri-State has said its transmission system is becoming more constrained. Outages rose last year, when electric sales reached a record 14 million megawatt-hours. That topped the previous record set in 2007 by 4.2 percent.

In March, Tri-State said it was working with Tempe, Ariz.-based First Solar Inc. to develop a 30-megawatt solar power plant in northeastern New Mexico, near Cimarron. It is expected to begin producing energy in 2010. The facility could eventually provide enough energy for about 9,000 homes.

Tri-State is investing in incentives for customers to use less energy and for the development of renewable energy, and it also is contracting for 220 megawatts of natural gas-based capacity in eastern Colorado.

It is still participating in coal-based carbon capture and sequestration projects.

“We will continue to make investments in research and development that preserve coal as an affordable, reliable and responsible resource option,” Anderson said. “We’re also pursuing innovations in energy efficiency, renewables and energy storage that bring value to rural electric consumers.”