National Guard helicopters, a C-130 aircraft with infrared equipment and scores of expert climbers were poised to launch the largest assault yet on Mount Hood on Saturday to locate three climbers missing since last weekend.

A C-130 made three passes over Oregon's highest mountain on Friday, but failed to find any sign of the three mountaineers.

Rescue workers — hindered all week by blizzards on the mountain — say they will make their largest effort on Saturday.

Hood River County sheriff's deputy Gerry Tiffany said the plan is to send teams of about 40 members each and helicopters up the relatively easy south side, hoping to reach the summit, and up the more difficult north side.

Blackhawk and Chinook helicopters were to arrive at Hood River Saturday morning. The Blackhawks may be used to drop rescuers onto the mountain's upper elevations.

Click here to view photos of the rescue effort

Authorities closed the upper elevations of the 11,239-foot mountain to everyone but searchers on Saturday to eliminate possible false clues from tracks or cell phones.

The C-130 Hercules, a heavy-lifting propeller-driven military workhorse capable of flying at slow speeds, was blocked by snow and clouds from any thermal hits that might have provided clues to the whereabouts of the three climbers, and the equipment also iced up, said Col. Jon Proehl, commander of the 152nd Airlift Wing of the Nevada Air National Guard, which provided the plane.

The plane made passes at 8,000 feet, 10,000 feet and the last at 12,500 over the top of Oregon's highest peak.

They were hoping to find a hint of two Texans and a New Yorker missing since one called family members on Sunday to report the party was in trouble and two members were descending for help.

The caller, Kelly James, 48, of Dallas, was in a snow cave when last heard from, his family said.

Mountaineering experts said that to survive, the climbers had to have dug good shelters.

Proehl said the C-130's equipment wouldn't have detected body heat from a snow cave in any case.

But the plane's crew spotted no sign of the climbers, such as a piece of clothing secured outside a snow cave.

Two climbers believed to have tried to descend the mountain are Brian Hall, 37, of Dallas, and Jerry "Nikko" Cooke, 36, of New York City.

The last clue to the climbers' whereabouts was a cell phone signal returned from James' cell phone on Tuesday.

After nearly a week of storms capped by one that knocked out power to hundreds of thousands of customers below the mountain, search and rescue teams were pinning their hopes on the C-130 and more favorable weather on Saturday.

"This is going to be probably an assault from all directions — south side, north side and helicopter," said Capt. Christopher Bernard of the Air Force Reserve's 304th Rescue Squadron, which is helping in the search.

Most of the searchers were pulled off of the mountain by Friday because of weather but some stayed at the Cloud Cap Inn, a a 19th-century former tourist lodge now used as a base by rescue workers at the 6,000-foot level. They hoped to get a fast jump if weather improved.

Bernard said the plan was to use helicopters to get searchers up the mountain as far and as fast as possible if the weather breaks to cut the time needed to get to where the snow cave is believed to be, near the summit on the north side.

He called the weeklong effort the most intense of his 19 years in search and rescue.

Steve Rollins of Portland Mountain Rescue, one of the volunteers helping in the search, said that after the storms and temperatures changes the snow on the mountain will be unstable — and the danger of avalanches great.

On Friday at a news conference, Bernard produced a handwritten note that said the climbers took food and such gear as fuel, bivvy sacks, a shovel and ropes, all of which could be helpful to survive.

The note was faxed to the sheriff's department last Sunday, the day the climbers were reported missing, said officials at the U.S. Forest Service ranger station above Hood River. But the list did not detail how much food the three had with them on the planned two-day quick climb.

On Friday morning, two wives and a sister of the climbers appeared on morning news shows.

"They're not quitters," said James' wife, Karen, as she locked hands in a single grip with climber Brian Hall's sister, Angela, and Michaela Cooke, wife Jerry "Nikko" Cooke.