Defense Secretary Robert M. Gates reassured U.S. war fighters in Iraq on Thursday that allowing gays to serve openly in the military will have little impact on the armed forces, an argument largely echoed by the top leaders of the Army, Navy, Air Force and Marine Corps.

Visiting troops at Camp Liberty in Baghdad, Gates was asked when repeal of the 17-year-old policy known as “don’t ask, don’t tell” would occur and what its effect would be.

“My guess is you won’t see much change at all, because the whole thrust . . . is you’re supposed to go on treating everybody like you’re supposed to be treating everybody now, with dignity, respect and discipline,” Gates told the troops. “And the same kind of military discipline that applies to — and regulations that apply to heterosexual relationships — will apply in terms of homosexual relationships.”

In Washington, leaders of the four services testified before the House Armed Services Committee on the implementation of the new policy. Several expressed reservations last December, when a divided Congress voted to repeal the law and President Obama signed the legislation.

The repeal did not occur immediately, as training and certification by the Defense Department are required before the ban is lifted.

Training for service members began about March 1 and is slated to be finished by the end of the summer.

Gen. James F. Amos, commandant of the Marine Corps, had testified last year that permitting gays to serve openly could disrupt smaller combat units and distract leadership from preparing Marines for combat. On Thursday, Amos said that during a recent trip to Afghanistan, he was specifically looking for potential problems.

“There hasn’t been the recalcitrant push-back, not been the anxiety of the forces in field,” Amos told the committee. He said one commander told him troops are focused on the enemy.

Last year, Gen. Norton Schwartz, chief of staff of the Air Force, had recommended waiting until 2012 to implement the policy.

He said Thursday that he was more comfortable with the policy now than he was in December. “We’re mitigating the risk the way we’re approaching this,” Schwartz said.

Adm. Gary Roughead, chief of naval operations, said training was going well and the “type of questions reflect the professionalism and the maturity and the decency of our people.”

Gen. Peter Chiarelli, vice chief of staff of the Army, said he met with commanders last Friday and “they indicated no issues so far.”

Nevertheless, Republicans on the committee have been critical of the policy change, with Chairman Rep. Howard P. “Buck” McKeon (Calif.) calling it a “rush to judgment.”

“The one outcome that must be avoided is any course of action that would put the combat readiness of our military forces at risk,” McKeon said.

Rep. Adam Smith (Wash.), the top Democrat on the panel, countered that forcing service members out of the military based on sexual orientation is far more disruptive.

“Gays and lesbians are currently serving in our armed forces, and we have the strongest military in the world,” Smith said. “Driving thousands of qualified individuals out of our armed forces under ‘don’t ask, don’t tell’ undermines our military’s effectiveness.”

Rep. Loretta Sanchez (D-Calif.) said she did not believe the military was “so fragile” that it could not deal with the new policy.

— Associated Press