KLAMATH FALLS, July 15 (Reuters) - Hand crews backed by water-dropping helicopters struggled on Thursday to suppress a huge wildfire that displaced roughly 2,000 residents in southern Oregon, the largest among dozens of blazes raging across the drought-stricken U.S. West.

The Bootleg fire has charred more than 227,000 acres (91,860 hectares) of desiccated timber and brush in and around the Fremont-Winema National Forest since erupting on July 6 about 250 miles (400 km) south of Portland.

That total was up 12,000 acres from Wednesday's tally. Firefighters extended containment lines carved around the blaze to 7% of its perimeter from 5% a day earlier, but were far from gaining the upper hand.

"This is going to continue to grow – the extremely dry vegetation and weather are not in our favor," Incident Commander Joe Hessel said on Twitter.

More than 1,700 firefighters and a dozen helicopters were assigned to the blaze, as the demand for personnel and equipment across the Pacific Northwest reached levels that have begun to strain available resources, said Jim Gersbach, a spokesman for the Oregon Department of Forestry.

"It's uncommon for us to reach this level of demand on firefighting resources this early" in the season, he said.

Firefighter Garrett Souza, a resident of the nearby town of Chiloquin, said Wednesday he and his team spent 39 hours straight on the "initial attack" of the fire last week.

"It's the cumulative fatigue that really, I think, wears a person out over time," he told Reuters, as he took a break from hacking at hotspots in the burn area.

No serious injuries have been linked to the Bootleg fire, officials said, but it has destroyed at least 21 homes and 54 other structures, and forced an estimated 2,000 people from several hundred dwellings placed under evacuation. Many have taken refuge in a Red Cross evacuation center at the Klamath Falls fairgrounds. Nearly 2,000 homes were threatened.