The agreement would resolve long-standing differences over the proper allocation of cheap hydropower from federal dams in the Northwest, backers say, and help defend the resource from envious electricity users outside the region.

And taking Bonneville out of the market for wholesale power will likely reduce costs for everyone, utility executives said in a letter mailed Thursday to Washington, Idaho, Montana and Oregon representatives and senators in Washington, D.C.

A delegation of 20 utility representatives will go to the nation's capital next week to explain the proposal in detail to members of the congressional delegation and their staffs.

Bonneville delivers about 40 percent of all electricity consumed in the Northwest. Existing contracts allot the power among utilities by "subscription," a process that forced Bonneville to buy power in wholesale markets because federal dams do not generate all that was demanded.

The result, exacerbated by a drought, was a rate increase of 46 percent last year.

The "slice" plan advanced by the utilities would divide whatever power Bonneville has among public utilities in the Northwest. A utility that takes 3 percent of the agency's power will pay 3 percent of its cost.

If the utility needs more power, it will have to find those supplies itself, or pay Bonneville to do the job.

Private utilities like Avista will not get power, instead dividing up $370 million in annual payments in lieu of power.

Avista receives about $12 million annually now for the exchange. Jeff Schlect, the company's manager for regional power issues, said that could increase under the new plan.

The Bonneville payments are credited to residential and small- business customers, whose rates were reduced 6.17 percent in Idaho and 7.41 percent in Washington.

Avista will be represented in Washington, D.C., by Schlect and Craig Gannett, a Seattle attorney who consults with the company on regional issues.

Schlect said the Northwest utility community has rallied behind the slice plan, but the owners of the region's aluminum smelters are not yet on board.

"We're hopeful we can develop a solution they can agree to," he said.

Only a few of the region's 10 smelters, which consume huge amounts of electricity, have resumed operations after more than a year of closure due to high energy costs.

More talks are also needed with environmental groups, Schlect said, adding that the utilities expect the final plan to preserve and reinforce the existing commitment to conservation and renewable resources.

Fish and wildlife safeguards will not be compromised, he said.

Bonneville Administrator Steve Wright has asked for four to six weeks to review the utility proposal.

If the outline is acceptable, Bonneville will begin a public review process this summer or fall, said spokesman Ed Mosey.

The agency would then begin to negotiate contracts with the utilities.

In an executive summary of the plan, the utilities say they need quick action in order to determine what new generating or conservation resources might be needed to meet consumer demand after Oct. 1, 2006, when most existing contracts with Bonneville expire.

A few utilities, including Inland Power & Light Co. and Kootenai Electric Cooperative Inc., have contracts that run into 2011.

"It's fairly early, but it's not too early," Mosey said. "It's time to start laying the groundwork."