SENATOR KENNEDY, in hs much-advertised speech at Georgetown yesterday, tried to have it all -- or at least to embody the whole range of political sentiments, from left to right, being aired in the country this year. Still, it was a useful nd clarifying speech, and we are glad Sen. Kennedy gave it. As candidates will, he spent an awful lot of time rejecting constraints (he had imposed upon himself) and talking about how he simply would not be stifled but would speak out and so forth, and we agree that he should. That's not the question: whether he or any other candidate should "speak out." The question is what they say when they do.

But a speech is, still, just that -- a speech, not something that exists apart from a speaker's 20-year-long record in public life, or that supersedes that record. And measured against his almost two decades in Congress, some part of the senator's Monday speech simply lacked credibility. It was that part in which he came at Mr. Carter from the right. Sen. Kennedy, the dedicated sponsor of a bank-breaking national health insurance program, is not credible in his new guise as budgetary scold, a lamenter over -- yes -- the size of the federal deficit. Nor is he credible in his charges that Mr. Carter has been too lax and indifferent about standing up to the godless Reds. Whatever Jimmy Carter's flaws in this regard, Sen. Kennedy has shared them and, in some cases, gone them one better.

In rehashing the sorry business about whether the shah of Iran should have been allowed into the country, Mr. Kennedy persisted in missing a rather large point. "He accepted the dubious medical judgment of one doctor that the shah could be treated only in the United States," the senator said of Jimmy Carter, and then: "Had he made different decisions, the shah would doubtless still be in Mexico, and our diplomats would still be going about their business in Tehran." The implications of this are staggering. What else should a president have to decide to do or not do to make sure that our diplomats are allowed to go about their business abroad? The point Sen. Kennedy just keeps sliding over is that the United States must be free to let into this country whomever it wishes to without making that decision continguent upon the desires or threats or demands of various terrorists.

Yet, apart from this clear break with the Carter policy, Sen. Kennedy's speech as it concerned Iran (and much else in the Middle East) was notable mainly for its similarity to administration thinking. The insistence that nuclear arms control opportunities be preserved, the emphasis on the importance of U.N. and other international backing for U.S. moves, the commitment not to abandon Israel under current pressures -- all this and more had a resonance in Mr. Carter's own various doctrines. Even the deal Sen. Kennedy proposed to get the hostages back is essentially the same one that the State Department is known to have been seriously negotiating for weeks now.

Still, when you have worked your way through the implausible attack from the right and the vast area of policy similarity to the president, you do come to the distinctive part, the places where the senator does take his stand consistently and in accord with what he has been for over the years -- the center of gravity of the Kennedy challenge to Mr. Carter. The senator is against the reimposition of draft registration and against the reinstitution of the draft. He believes the defense contractors and the "military-industrial complex" generally stand to profit from Mr. Carter's tough stand, at the expense of everyone else, that the social programs have been slighted by Mr. Carter in his state of the Union message, that our energy and economic nightmares must be dealt with by federal government intervention: gas rationing now and the imposition of wage, price, profit controls.

Sen. Kennedy has more faith than we do in the potential of laws and rules and directives to control and tame these things. But that is an argument for another time. What he has done is to identify the nature of his candidacy, the feelings of his constituents and the policy issues he really cares about. Speaking for the discontented liberal-left of his party, Mr. Kennedy does not suffer a lack of credibility. Somehow, minus the ill-fitting and newly acquired neo-conservative garb and despite the closeness of some of his views to those of Mr. Carter, the senator has managed at last to suggest what he is doing in this race.