And if Congress fails to adopt the deficit-reduction recommendations of a bipartisan joint Congressional committee this fall, the Defense Department will be required under debt ceiling legislation passed in August to find about $900 billion in savings over the coming decade. Cuts that deep will almost certainly entail reducing personnel benefits for active and retired troops, Pentagon officials and analysts say.

“We’ve got to put everything on the table,” Defense Secretary Leon E. Panetta said recently on PBS, acknowledging that he was looking at proposals to rein in pension costs.

Under the current rules, service members who retire after 20 years are eligible for pensions that pay half their salaries for life, indexed for inflation, even if they leave at age 38. They are also eligible for lifetime health insurance through the military’s system, Tricare, at a small fraction of the cost of private insurance, prompting many working veterans to shun employer health plans in favor of military insurance.

Advocates of revamping the systems argue that they are not just fiscally untenable but also unfair.

The annual fee for Tricare Prime, an H.M.O.-like program for military retirees, is just $460 for families and has not risen in years, even as health care costs have skyrocketed. Critics of the system say the contribution could be raised substantially and still be far lower than what civilians pay for employer-sponsored health plans, typically about $4,000.

Those critics also argue that under the current rules, 83 percent of former service members receive no pension payments at all — because only veterans with 20 years of service are eligible. Those with 5 or even 15 years are not, even if they did multiple combat tours. Such a structure would be illegal in the private sector, and a company that tried it could be penalized, experts say.