Brace yourself for a new blast of Washington jargon: non-means-tested entitlements. In less fancy language, that means Social Security, Medicare and the other federal retirement and disability programs where the benefits you get do not depend on the level of financial need you can demonstrate. The escalating costs of those programs are coming seriously into question.

The first step in the battle is the current effort to halt the drain on the Social Security trust fund by advancing tax hikes and slowing down future benefit increases. The package of legislation designed to do that job should clear Congress this month.

But coming along right behind it is an even meaner fight over Medicare. As Senate Budget Committee Chairman Pete Domenici warned the nation's governors the other day, "Medicare can be bankrupt in 21/2 years," unless some way is found to put the brakes on its burgeoning costs.

And unlike Social Security, which can look forward to a 30-year period of improving balance as the baby-boom generation takes its place in the world of work, "Medicare has no demographic amelioration," Domenici pointed out. "It does not get better with the passage of time."

Even before they heard Domenici's stark warning at their meeting in Washington, the governors had drafted a resolution that put them on the record, for the first time, as calling for a restraint on the growth of these entitlements.

That part of their budget resolution drew less attention than their call for a slowdown in the pace of the Pentagon buildup--also a first for them. But it was an equally important step, for the governors, two-thirds of them Democrats, to say that such political "untouchables" as Social Security and Medicare can no longer remain untouched.

Richard S. Williamson, the president's assistant for intergovernmental relations, said he welcomed that recognition--which, indeed, was overdue. By leaving such huge programs as Social Security and Medicare essentially untouched by the first two rounds of President Reagan's economies, the administration and Congress forced severe slashes in the very programs that are of most importance to the poor: food stamps, Medicaid, subsidized housing, public service jobs, Aid to Families with Dependent Children.

For all their complaints about Reagan's allegedly "ripping the safety net," Democrats have been no more eager than Republicans to go after programs such as Social Security and Medicare with their huge middle-class constituencies.

That does not mean there are not important partisan and policy differences in the way in which the needed restraint is applied. One of the Democratic governors, Bruce Babbitt of Arizona, pointed out those differences in a speech the other evening.

The president, Babbitt pointed out, "is proposing to double the Medicare deductible from $200 to $400 and to triple the Part B physician's care premium from $200 to $600 for all Medicare recipients, rich and poor alike. The result is a regressive change that will impose more hardship on the poor, while scarcely affecting the wealthy, for whom a few hundred dollars a year is of little consequence."

Babbitt suggested that a fairer way to do it would be to raise the deductible by graduated amounts for those among the retired whose adjusted gross income is more than $20,000--the same level at which the compromise Social Security package would make Social Security payments deductible.

Babbitt would go further, by declaring that all the entitlement programs should be subjected to means-testing. He acknowledged to his Princeton University audience that many of his fellow Democrats would rebel at such a notion, which, in their view, contradicts the very concept of "entitlements."

But he made a point that has to be weighed seriously by Democrats. In his view, as in my own, the Reagan election of 1980 was no freak or aberration, but rather the inevitable result of a period of virtually unrestrained growth of government-- particularly in the entitlement program area. The tripling of the share of the total economy that was devoted to those entitlement programs between 1965 and 1980 created "a backlash" that is, in his words, "the real, enduring meaning of the election of 1980."

If you accept that proposition, then Democrats have no choice but to enter the policy debate on the best way to slow down that growth. That is what the governors did last week--and it was a significant action.