Duke Energy and Progress Energy filed a new plan Wednesday to save their planned merger, telling state regulators they would spend up to $150 million on new transmission projects and contract to sell electricity to wholesale buyers.

The N.C. Utilities Commission has up to 30 days to review the plan, which then goes to the Federal Energy Regulatory Commission. The federal agency's concerns over the merger's effects on competition for wholesale power prompted the new filing.

Duke and Progress hope a third offer - after FERC rejected merger plans in September and December - will allow the $26 billion deal to close by about midyear. They had initially aimed for the end of 2011.

"What we're offering today is designed to address specifically what FERC said we needed to address in December," when it rejected the utilities' previous plan to resolve competition concerns, said Duke spokesman Tom Williams.

Duke and Progress also have to satisfy state regulators, who will focus on keeping customers from paying for merger costs. The companies said they will work with the N.C. Public Staff and South Carolina's Office of Regulatory Staff, which advocate for consumers, to resolve rate issues before sending the plan to FERC.

"The intent of this merger is to strike the right balance between the customer and shareholder benefits, and that continues to be our goal," Duke CEO Jim Rogers said in a statement. Duke and Progress have said the merger will save Carolinas customers $650 million in the first five years.

As a permanent fix of the competition problems, the utilities said they will build new transmission projects to expand the ability to bring more wholesale power into the Carolinas from other producers. The projects would cost about $75 million to $150 million.

The plan outlines three initial projects, including updated transformers and new lines.

While those would reduce the utilities' grip on wholesale markets, it said, some concentration problems would still exist in Progress' eastern North Carolina territory. To address those problems, the companies may offer five additional transmission projects there.

As those projects are under construction, over about three years, the companies will also sell wholesale power to third parties.

Unlike the previous plan, which offered power that had no guarantee of buyers, the utilities say they expect to sign contracts with buyers before filing the merger plan with FERC. Negotiations are under way, they said. The plan "will have no adverse impact on rates or service" to current customers, the N.C. Utilities Commission filing said.

The utilities say they can offer the wholesale power without hurting their ability to serve existing customers. Importing new energy through the transmission projects, the filing added, "will ultimately increase the availability of lower cost power in the Carolinas, thereby benefiting retail customers."

It's likely to be May before FERC rules on the merger, Rogers told financial analysts last week. The N.C. commission would then have to approve the union, and South Carolina's commission has to accept a joint-operating agreement between Duke and Progress. If approved, the new Duke Energy would be the nation's largest utility, with 7.1 million customers in six states.