Washington (CNN) -- Preparations for repealing the "don't ask, don't tell" policy that bans openly gay people from the military have gone better than expected so far, military leaders told a House committee Thursday.
"I've been looking for issues, but honestly we haven't seen it," said Gen. James Amos, the U.S. Marine Corps commandant who was perhaps the most resistant of the military chiefs to the repeal measure passed by Congress in December.
"There hasn't been the recalcitrant pushback," Amos added. "We haven't seen the anxiety over it from the forces in the field."
Amos confirmed that roughly 60 percent of Marine combat fighters had expressed concerns about the repeal in a survey conducted last year amid a prolonged congressional debate.
On a recent trip to Afghanistan, Amos said, he asked combat forces about any concerns and learned that "they're focused on the enemy" rather than the repeal issue.
Army Vice Chief of Staff Gen. Peter Chiarelli offered a similar assessment, saying no major issues had been raised during training sessions for Army troops.
However, Chiarelli and Air Force Chief of Staff Gen. Norton Schwartz both cautioned that it will take time to complete the full training and other preparations to implement the repeal.
"We must continue to do this deliberately," Chiarelli said. "Training is just the start. ... The entire process, done properly, will take time."
Schwartz said he is "more comfortable" with the repeal process than he was in December, when Congress passed the measure, "but we still have a ways to go."
The repeal can occur only after President Barack Obama, the defense secretary and the chairman of the Joint Chiefs of Staff certify that it won't harm the effectiveness of the military. Once certification occurs, there will be a 60-day period before implementation.
Certification will depend in large part on assessments by the military leaders who appeared Thursday before the House Armed Services Committee.
Their comments indicated it would be several months at least before they would be prepared to declare their forces ready for the repeal to take effect.
According to the commanders, all the training should be completed by the end of June.
Amos made clear he will be unwilling to certify Marine readiness until all the necessary training is complete, and his commanding officers indicate troops are ready.
In a letter to the committee, Army Chief of Staff Gen. George Casey, who missed the hearing due to the recent death of a grandson, said he still has concerns about the overall impact of repealing "don't ask, don't tell."
"I believe it is too early to say what the impact on implementation of the repeal of DADT will have on our morale, unit cohesion, good order, discipline, recruiting and retention in the Army," Casey wrote. Overall, Casey's letter said, he believes implementation of the new policy can be accomplished with what he called "moderate risk to military effectiveness and the long-term health of the force."
At the same time, Casey said he personally led training of the Army's top generals and has talked to leaders at different levels who "found the guidance simple and effective and were often surprised by how little had actually changed."
One committee member, Republican Rep. Vicky Hartzler of Missouri, pleaded with the military chiefs to reject the repeal.
"I want to challenge you that you are the last force to be able to stop this onerous policy," Hartzler said of the repeal. "And I have to believe from my heart in your gut you know this is not the right thing. I appreciate that you follow command, you follow the Constitution and you are fulfilling what you are charged to do, but there is an opportunity to not certify this and it has fallen on you at this time in history to be able to give the final say."
CNN's Charley Keyes and Tom Cohen contributed to this story.