By Tabassum Zakaria

WASHINGTON (Reuters) - Even senators are bridling at new airport security measures that include highly personal patdowns of some passengers that a top transportation security official acknowledges are invasive.

As the busy holiday travel period approaches, senators at a hearing on Wednesday complained to Transportation Security Administrator John Pistole about the tougher screening which entails a patdown or highly detailed body imaging.

"I'm wondering why I got both a few weeks ago. I did use my Senate I.D. and was subjected to both," Republican Senator Mike Johanns said during a Senate Commerce, Science and Transportation Committee hearing. "Now, I didn't object to going through the advanced imaging."

The new airport screening procedures come after several foiled plots in the past year, including a Nigerian man who tried to detonate explosives hidden in his underwear aboard a U.S. flight from Amsterdam to Detroit in December.

Republican Senator George LeMieux expressed worries about the degree of contact in the patdowns, which include touching of the genital region and breasts.

"I'm frankly bothered by the level of these patdowns. I've seen them first-hand in airports in Florida," he said.

"I wouldn't want my wife to be touched in the way that these folks are being touched. I wouldn't want to be touched that way. And I think that we have to be focused on safety, but there's a balance," he said.

Pistole agreed it was important to strike the right balance between safety and privacy, but said most travelers want to fly on a plane with passengers who had been properly screened.

"I recognize the invasiveness of it. I also recognize that the threat is real. The stakes are high, and we must prevail," Pistole said.

SOME RANDOM PAT-DOWNS

Pistole sought to address a public backlash, saying the patdown usually occurs only if an alarm goes off during the full-body scan or metal detector, or if passengers opt out of the scan.

"It would be a very rare instance for somebody to have a patdown if there wasn't some type of alarm," Pistole said, adding he would look into Johanns' report that he received both.

A "very, very small number" of patdowns are done randomly, he said, "so we can be unpredictable to the terrorists."

Almost 400 body scan machines have been deployed in U.S. airports, while some airports still use only metal detectors. After a flood of complaints, TSA eliminated patdowns for children under 12 and will develop other procedures for pilots who already undergo extensive security checks.

The travel industry is concerned that Americans will cancel trips and further hamper a still fragile economy.

"Air travel is the gateway to commerce and job creation in the United States," said Roger Dow, president of the U.S. Travel Association, in a statement.

Last month, explosives were discovered hidden in packages aboard cargo flights to the United States. The Yemen-based militant group al Qaeda in the Arabian Peninsula has claimed responsibility for the plots.

Pistole said security screening is "uneven around the world." When he was in Yemen two weeks ago he found that their cargo screening relied almost exclusively on X-ray machines.

"And it's not a modern, advanced technology X-ray machine, where you can see two dimensional things like that. No explosive trace detection, very limited physical inspection, no canines," he said.

As for the coming holidays, Pistole offered the following advice to air travelers: "Come prepared. Look at what the screening protocols are, and treat it as a partnership."

(Reporting by Tabassum Zakaria; Editing by Cynthia Osterman)