The effort to overhaul the military retirement system is entering its final phase after the Pentagon's top brass has offered a detailed critique of the legislation that is winding its way through Congress.

Overall, the members of the Joint Chiefs of Staff support the current proposal but have some concern about its potential impact on retention of career troops and want to ensure the new rules do not cut the overall real value of the retirement benefit for those who serve 20 years or more.

"What we're worried about is: Don't reward people who stay less than 20 by hurting people who stay more than 20," Air Force Chief of Staff Gen. Mark Welsh said in a May 21 "virtual town hall" meeting with enlisted airmen. A video of his remarks was posted online.

"We want people still to stay in and serve a career in the Air Force, so the longer you stay, the more benefit the plan should be to you," Welsh said.

The Joint Chiefs recently finalized a set of recommendations for the retirement system and forwarded it to Defense Secretary Ash Carter, who is expected to send similar views to the White House and ultimately Congress later this summer.

The proposals on Capitol Hill call for reducing the size of the fixed-benefit pension by about 20 percent and adding a 401(k)-style benefit that would create individual retirement savings accounts that most troops would own and keep regardless of whether they serve a full 20-year career.

That would amount to a generous new benefit for the vast majority of the force that does not reach 20 years of service and now receives no retirement benefits.

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Yet the chiefs are reluctant to cut the real value of the current benefit for those career troops who do serve long enough to retire. The brass wants to make sure the new benefit for those who serve more than 20 years — the combination of the smaller pension and the government contributions to the individual investment accounts — remains roughly unchanged.

"They think that the level of compensation right now is about right," said one defense official familiar with the high-level discussions who spoke on condition of anonymity. "They are trying to work through all the numbers so that if we do this blended retirement system, that it is truly equitable, not smoke-and-mirrors equitable."

Another key change recommended by the Joint Chiefs, Welsh said, is to extend the government contributions to individual retirement savings accounts for their entire length of service.

The initial proposal suggested that those government contributions should stop at 20 years of service, even if the member continued to serve longer.

"That made no sense to us," Welsh said.

The new retirement proposal on Capitol Hill would create investment accounts under the existing Thrift Savings Plan for all troops entering service. Money deposited into a TSP is not available for withdrawal without a tax penalty before age 60.

The government would immediately begin making annual deposits equal to 1 percent of a member's basic pay. After two years of service, those accounts would "vest" and ownership legally transferred to individual service members for them to keep whenever they separate.

In addition to that 1 percent deposit, the new deal calls for the government to match dollar-for-dollar, up to 5 percent, any additional contributions that troops voluntarily make to their savings accounts from their own pay.

Welsh also said the chiefs will recommend that the individual contributions and the dollar-for-dollar match should not begin until after a service member completes his or her first term of enlistment.

"You should not be able to up your matching to 5 percent until you re-enlist the first time, and that way you actually think through: How much of your money do you really want to put in this TSP account?" Welsh told airmen during the virtual town hall meeting.

The push to reform military retirement gained steam in January after the Military Compensation and Retirement Modernization Commission unveiled the results of a two-year study and a slate of detailed recommendations for Congress. Lawmakers have expressed support for the retirement proposal.

The commission's members say their proposal ultimately would provide a better deal for everyone, saving the government money, giving short-term troops a new benefit and providing careerists with more value in the long run.

But many veterans service organizations have questioned the claim that the original proposal offers a better deal for career troops.

Welsh said the Pentagon's official response to the retirement proposal has taken longer than planned because the chiefs did not understand the analysis that the commission initially provided.

"There were some details in there that we don't really understand because the numbers weren't adding up when we looked at the numbers that the commission gave us," Welsh said.

"So the intent on our side is to get all the details from the commission and make sure we have kind of the calculator right on this and then ship a bunch of examples out to you so you can see it," Welsh said.

A grandfather clause will allow today's troops to decide whether to opt into the new system and begin accruing money in an individual TSP or, if they prefer, remain under the current system that promises bigger lifetime payments for those who ultimately reach the 20-year mark, Welsh noted.

"If you know you're going to get out before 20 years, the new plan is great," he said.

Then Welsh added: "Those of you who aren't sure, stick with the old plan. You know what you got."

Staff writer Jeff Schogol contributed to this report