BOSTON -- The chief executive of New England's power grid manager warned Tuesday that a growing regional dependence on natural gas, combined with supply constraints, is threatening its ability to guarantee electricity whenever and wherever it's needed.

Gordon van Welie of ISO New England testified in Washington, D.C., before a House subcommittee that "the status quo is unsustainable."

Van Welie said the region now gets just over half its power from natural gas and nearly a third from nuclear power.

A switch to lower-cost, lower-emission natural gas -- which also is widely used regionally for heat -- has major economic and environmental benefits, he said. But it's straining the existing pipeline infrastructure, which isn't sufficient to allow New England full access to abundant gas supplies from the west and south.

The effect of the bottleneck was seen this winter in a price increase. Van Welie noted that in late January, New England was paying more than eight times what other regions were paying for natural gas.

A massive storm in February, which was accompanied by widespread power outages, also highlighted problems, he said.

Van Welie said at one point, 6,000 megawatts of electricity -- about a fifth of the region's total capacity -- wasn't available, in part because gas generators couldn't find fuel.

That showed a clear need for more flexibility in the gas supply system, since the gas market operates only on weekdays, and it was a weekend storm, van Welie said.

But he also emphasized the need to beef up fuel inventory, such as by building more storage facilities, making contracts with liquid natural gas suppliers and investing in pipelines, including those that can carry two fuels, such as oil and gas.