As powerful Hurricane Rita aims at Texas and threatens to bring more misery to the Katrina-battered Gulf Coast, relief organizations are straining to keep up with the multiplying demands on their supplies, equipment and manpower.

The Southern Baptists have run out of portable shower units for hurricane-affected areas. The Presbyterians have turned to the Norwegians for advice on housing evacuees. And some shorthanded Red Cross chapters are struggling to set up shelters they just dismantled.

"It's just unbelievable," said Margaret O'Brien-Molina, a spokeswoman for the American Red Cross's southwest service area, which is bracing for another massive shift of people as Rita arrives. "There is so much need out there, and getting the volume of people -- the number of staff -- up to what we need . . . is difficult."

Most domestic relief organizations launched their biggest efforts ever to respond to Hurricane Katrina and are having to dig deep to find resources for the latest threat looming in the Gulf of Mexico. The hurricane could reach Texas late tomorrow or early Saturday, according to predictions.

"It's certainly challenging," said Joe Conway, a spokesman for the Southern Baptist Disaster Relief program, which has deployed more than 6,000 volunteers from 36 states into the area affected by Hurricane Katrina.

Conway said that all of his program's mobile shower units -- trailers with as many as eight shower stalls -- are on site in Katrina-affected areas. And more than half its fleet of other disaster units -- including mobile kitchens, chain saw units, laundry facilities and mobile child-care centers -- have been deployed to the Katrina area.

Already, Conway said, the organization has served 3.6 million meals, surpassing the previous record of 2.5 million meals after Hurricane Andrew in 1992.

To keep up with the demand for volunteers, Conway said, the organization had a mass training of volunteers in Texas two weeks ago and has another scheduled in Georgia.

Presbyterian Disaster Assistance has sent 36 trained disaster-response specialists into the Gulf region to help local churches respond and, if they're affected by it, help get them running again.

That leaves only four to deploy in the wake of Rita, said John Robinson, associate for national disaster response for Presbyterian Disaster Assistance, an arm of the Presbyterian Church of the USA.

"We're stretched a bit thin," Robinson said.

The church is setting up 15 camps of 150 volunteers each in the disaster area but is short of camp managers, he said.

Beyond that, Robinson said, "we need tents, shower units, and if anyone's got some good ideas for insulated tents, I'd like to know."

Currently, 97,000 Katrina evacuees remain in shelters in 27 states. But as hundreds of thousands of people are moved away from the Texas and Louisiana coasts, those number are expected to soar again.

In Alexandria, La., which sheltered 7,000 evacuees from the New Orleans area after Katrina, exhausted Red Cross officials are setting up shelters they just shut down, readying for another influx of hurricane evacuees.

Some of them will be the same people -- New Orleans area residents who fled to Alexandria during Katrina but then returned to their homes in recent days as the floodwaters receded.

"We're going to see a lot of people just driving back to the shelters where they were," predicted Leann Murphy, chief executive of the central Louisiana chapter of the Red Cross in Alexandria.

The sheer volume of displaced people -- more than a million so far, before any Hurricane Rita evacuees are counted -- has compelled some relief groups to turn to international relief organizations that are more accustomed to aiding millions of refugees, said Susan Kim, news editor for Disaster News Network, a news service funded by relief organizations.

"It's the scale of this that is really the problem, the sheer volume of people," Kim said.

Presbyterian Disaster Assistance, for example, got help from Norwegian Church Aid on situating shelters and getting them up and running, Robinson said.