STONEHAM, Texas — State fire officials said Tuesday they are seeking federal help in fighting wildfires that have forced hundreds of residents to evacuate and blackened tens of thousands of acres in forested East Texas.

The Texas Forest Service said a federal management team is needed to help coordinate efforts in Polk and Trinity counties, where a 20,000-acre blaze is burning. Assistance was also sought for a 3,500-acre fire in Jasper County.

Because of a shortage of aviation resources, four National Guard Blackhawk helicopters and two Chinooks have been activated, the forest service said.

The request for federal assistance didn't include a 5,000-acre fire in Grimes County, about 60 miles northwest of Houston. The blaze had already burned about a dozen homes before it jumped containment lines Monday, leading to the evacuation of about 1,800 homes and businesses.

Help could be on the way, though. Rain was in the forecast Tuesday, with light showers falling in parts of the Houston area.

The fire in Polk and Trinity counties was 60 percent contained, and officials were optimistic that weather conditions would help firefighters, said Texas Department of Public Safety spokesman Greg Sanches.

"The humidity is up," Sanches said. "We're just kind of waiting to see what's going to happen."

The East Texas fires are among 22 large blazes the forest service is handling across the drought-stricken state, and they have burned nearly 135,000 acres, according to agency figures.

All but 28 of the state's 254 counties had outdoor burn bans in place Tuesday, and more than 3 million acres have been torched since the Texas wildfire season began in November, the forest service said.

Scarce rain and low humidity have fueled conditions in southeast Texas, where heat is common but the ground in the heavily forested area usually remains moist. Brisk dry winds more associated with West Texas buffeted the area Monday.

At least seven mobile homes were burned in a 150-acre Kendall County fire in Central Texas that also led to mandatory evacuations of a subdivision and a park for recreational vehicles.

In the Texas Panhandle, where wildfires killed a firefighter earlier this year, three firefighters sustained minor injuries battling a blaze south of Amarillo.