TRYING HIS BEST to impale viewers with his cold blue-eyed Oval Office stare and firm-voiced Leader of the Free World righteous indignation, Jimmy Carter lashed out at his primary Democratic opponent last Wednesday night.

In doing so, he showed the symptoms of a curious disease that afflicts Presidential contenders who unexpectedly find themselves in an ostensibly commanding position. Call it "The Perils of Prosperity," after the book, or "The Paradise Syndrome," after the Star Trek episode; however described, the arrogance of front-runnership can be dangerous--and Jimmy Carter has a bad case of it.

At his first press conference since November, Carter responded to two criticisms from Sen. Edward M. Kennedy '54 (D-Mass); specifically, that Carter had come over only lately to the idea of a commission to settle the Iranian crisis and that Afghanistan "might not have happened" if the President had shown the Soviets more resolve and paid more attention to the signs of impending invasion.

"It's not my inclination to respond to every allegation--erroneous allegation--that Senator Kennedy has made," Carter began. So far, psychologically correct: a continuation of the Rose Garden strategy that has proved so effective and so desperately frustrating to Kennedy, Carter had maintained the cool, unflappable image of a leader above the fray.

But then he lost control; political impulses, carefully repressed and sublimated in public even while the hot-line burned between Washington and Des Moines, Portland and Manchester, got the best of him. Kennedy's statements, he went on, "have not helped our country." When the hostages were originally taken, Carter said.

Senator Kennedy insinuated that because we had given medical treatment to the Shah that somehow the seizure of our own hostages was not the fault of the terrorists who took them, but the fault of the United States.

Senator Kennedy has also said that the invasion of Afghanistan was not only not very serious but that somehow or another the Soviets were not the culpable party, but the United States was at fault, and somehow caused or contributed to the Soviet invasion of Afghanistan.

And more recently, he has insinuated--again falsely--that some action or lack of action on my part or the United States' part had perpetuated the incarceration of American hostages.

The thrust of what he said throughout the last few weeks is very damaging to our country, and to the establishment of our principals and the maintenance of them, and the achieving of our goals to keep the peace and to get the hostages released.

When people expect the worst from a president, an adequate or mediocre response takes on an aura of grandeur; Carter seduced the national press ("lights at the White House burned into the night") as effectively as he did the voters of Iowa. Carter appreciates how wide his support has become, but not how thin it remains. By going for the jugular, he hoped to capitalize and exploit the popularity he has gained by not going off the deep end over the past four months, which in these times passes for a substantial accomplishment. Yet when so minor an achievement can inspire the dramatic turnabout of political fortunes witnessed since Iran--Kennedy's two-to-one lead now reversed--it reflects a shallowness of commitment to either candidate rather than firm support for one.

The frontal assault on Kennedy showed that Carter does not perceive this. He not only believes the polls, he trusts them, and felt some sharp thrusts at Kennedy's patriotism would bury him (not to mention having press secretary Jody Powell charge him with an "unrestrained display of political ambition," of all things).

But pulling the plug on Kennedy's candidacy is a delicate operation, one that Dr. Carter may be in the process of botching. Overestimating his support and the leeway it gives him, Carter revealed his vulnerability last Wednesday; he played right into Kennedy's hands by allowing himself to be baited into a shouting match that either side may lose. Carter went for the kill; the result was overkill.

THE SIGNS OF IMMINENT TROUBLE for the current front-runner loom elsewhere. Carter campaigners are less than adept at poor-mouthing--reducing expectations so the results look good. Immediately after Iowa, political wisdom had it that Kennedy would be out of it if he didn't win both Maine and New Hampshire. yet his competitive defeat in the Maine caucus ended up as a moral victory, and now Carter is in the historically unenviable position of heading the pack into New Hampshire. Lyndon Johnson needed a big win here in 1968, Ed Muskie in 1972; Eugene McCarthy and George McGovern refused to give it to them, and the campaigns turned in favor of the two narrow losers. Unless Carter repeates his Iowa performance, gaining a majority, the momentum will shift.

Voters do not like to be taken for granted. Dealt a political straight flush in a card game no one understands, Jimmy Carter may be overplaying his hand. He's already shown he can't keep a poker face.