After challenging the Carter administration's proposed health budged as too stingy, Sen. Edwad M. Kennedy (D-Mass.) yesterday released a pointed criticism of the administration's defense budget, too.

In a press release, Kennedy charged that the White House had juggled its figures to claim that defense spending would go up 3.1 percent next year after allowing for inflation. In fact, Kennedy charged, the true figure would be more than 4 percent, and would be too high.

Kennedy's figures were based on a close reading of the budget by several outside experts. Informed sources said Kennedy's aggressive staff had been canvassing experts ofr several days gathering detailed information on the Carter budget.

Kennedy is reliably said to feel that the cutbacks in health programs that he finds unwarranted could easily be restored with money trimmed from the huge defense budget, and that the Pentagon's proposed 1980 outlays of $125.8 billion may be the only significant potential source of extra cash in the tight administration budget.

In his press release yesterday, Kennedy said he would support a 3 percent increase in defense spending for the NATO alliance, but that the across-the-board increases proposed by the administration were excessive.

He specifically criticized the $1.6 billion aircraft carrier the administration has proposed as a substitute for the $2 billion-plus atomic carrier that President Carter vetoed last year. The carrier is unneeded, Kennedy said.

He also quetioned the usefulness of the proposed new MX missile, calling it a weapon that could "increase the threat of nuclear war" because of its size and accuracy, which might intimidate the Soviets into firing first in some future nuclear confrontation.

Kennedy accused the administration of padding its estimates to arrive at the 3.1 percent figure for the increase it proposes for defense spending. (In fact, the actual increase in the budget is 11 percent; the 3.1 figure is based on deducting the impact of inflation in the last year).

Administration officials acknowledged that they had included in their estimate of last year's defense spending $2.2 billion that actually has not been appropriated yet. These funds are included in a supplemental appropriations request that only reached Congress this week. Assuming that $2.2 billion is appropriated (and congresional sources say it will be), then the $125.8 billion proposed for next year would be about 3.1 percent higher than this year, after discounting the effects of inflation.

"We must give this one quarter of our budget the same close scrutiny as we give to nondefense programs," Kennedy said.