As the U.S. Air Force faces one of the biggest sex abuse scandals in recent military history, the officer tapped to be its newest chief of staff blasted its uphill battle to crack down on sex crimes.

"What we have been doing is not working," said Gen. Mark Welsh III, in his nomination hearing before the Senate Armed Services Committee today. "Everyone is trying to do the right thing and figure out some way of stopping this. But the fact is, we haven't."

If confirmed, Welsh would become the Air Force's top uniformed officer, taking the reins at a time when "horrible" sex abuse allegations are rattling the force.

An ongoing investigation found that since 2009, at least 31 female recruits were alleged victims of sexual misconduct and rape by some of their male drill instructors at Lackland Air Force Base in San Antonio, Texas.

Lackland is the Air Force's largest boot camp training facility, with about 500 instructors - 12 of whom are currently under investigation. Six of these are facing criminal rape, adultery and aggravated sexual assault charges, including one who pled guilty in April to having an inappropriate relationship with a trainee.

The scandal took center stage again Tuesday, when court-martial testimony began against Staff Sgt. Luis Walker, who has the most serious case with 28 counts. Walker is charged with raping or sexually assaulting 10 female trainees, and if convicted, could receive a dishonorable discharge and a life prison sentence.

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Four of Walker's alleged victims took the stand yesterday, some fighting back tears as they described him luring or forcing recruits into sexual favors, then demanding they not tell anyone. Closing arguments in his case are expected this afternoon.

Welsh deemed this type of behavior "unacceptable." He noted the Air Force has put measures in place in attempt to reduce sexual assault - like offering institutionalized and refresher training for all members, and hiring more investigators who specialize in sex cases.

But as the investigation grows, Welsh said what's missing is a way to identify perpetrators and stop sex crimes before they even occur. For instance, better screening of new enlistees could help weed out potential criminals, or harsher punishments for low-level crimes could serve as a deterrent.

"The simple fact is, the goal for sexual assault in the United States Air Force … is not a declining trend. It's zero," Welsh said. "Anytime this happens, it's horrible. And we're not doing enough to stop it."

Welsh's nomination hearing comes on the heels renewed calls from Congress to take action. Last week, 77 Congressmen signed a letter demanding a House investigation of sex abuse at Lackland, calling it a "systematic" and "alarming" trend. The House Armed Services Committee has not yet responded.

The Air Force is also receiving flak from Capitol Hill for its proposed budget for fiscal year 2013, which would cut nearly 10,000 personnel and could force several flying units to be grounded. With the defense sequester also looming as part of the so-called " taxmageddon," the military would see another $500 billion in budget cuts - a fate that Defense Secretary Leon Panetta warned would be "catastrophic" to the armed forces.

Welsh echoed the dire prediction today, saying a predicted 14 percent budget cut across the board would affect everything, from personnel readiness to equipment to counterterrorism activity.

"The impact is almost immediate," he said.

Welsh is currently the commander of U.S. Air Forces in Europe. In May, Panetta nominated him to replace Air Force chief of staff, Gen. Norton A. Schwartz, who is retiring Oct. 1 after four years at the post.

Welsh graduated from the U.S. Air Force Academy in 1976 and has since logged more than 3,400 flight hours in his rise to general. He recently worked at the CIA under then-director Panetta, where he was the associate director for military affairs.

No date has been set for Welsh's nomination vote in the Senate.