Jack Kemp and Ted Kennedy don't agree on many things. But when the conservative Republican from Buffalo and the liberal Democrat from Boston start to sound the same note, you can safely conclude that the whole political orchestra will soon be playing that tune.

If so, Paul Volcker and the Federal Reserve Board better get ready to become the political scapegoats for this stubborn and severe recession.

Kemp signaled his unhappiness with a fairly dramatic -- but not widely noted -- protest gesture. The week before last, when the Republican budget backed by President Reagan was finally going through the House of Representatives, Kemp voted no.

He waited until the last minute, because, as he said, "I did not want my vote to defeat Reagan's budget." He did not speak on the floor, because as the chairman of the House Republican Conference, he did not want to embarrass the other leaders.

But for all the protocol he observed, Kemp's vote was no casual thing. The ardent apostle of across-the-board tax cuts, the man who helped sell Reagan on Reaganomics was publicly washing his hands of the current policies.

A few days after the vote, he told me: "I fought for the last six months, inside the administration and the leadership meetings on Capitol Hill, and I lost, so I finally decided I had to stand aside and say no."

Kemp objects to the $20 billion in tax increases in the GOP budget -- which he says will jeopardize the chances of an economic recovery and "hurt the working people who ought to be our constituents."

But even more, he believes that there will be no real economic recovery -- just "a modest lift" in late summer -- unless and until the administration tackles "the fundamental crisis in monetary policy." Kemp says that will require Volcker and the Federal Reserve Board he heads to rescind the momentous policy change they made on Oct. 6, 1979.

A couple days after Kemp had cast his "no" vote and given me that explanation, Kennedy was lashing out at exactly the same target in the pages of The Boston Globe.

"In October, 1979," he said, "Federal Reserve Board Chairman Paul Volcker announced that henceforth the Fed would conduct its business with only one objective in mind -- to control the growth in the money supply . . . .The Fed abandoned its concern with interest rates; it would no longer use its powers to ensure that credit would be available or affordable. The results have been ruinous."

Last Tuesday, Kennedy took up the campaign in a face-to-face encounter with Volcker at a hearing of the congressional Joint Economic Committee, demanding to know how long "are you going to keep grinding the economy down?"

Nor was he alone. Volcker was hazed by liberal Democrat Henry Reuss of Wisconsin, moderate Democrat Lee Hamilton of Indiana, liberal Republican Peggy Heckler of Massachusetts, moderate Republican Bud Brown of Ohio and conservative Republican Paula Hawkins of Florida.

They disagree on the remedy. Kemp and others think we have to reestablish some link between the dollar and gold. Kennedy and his friends favor some kind of credit-allocation scheme. But they all make the same criticism of current Fed policy: Inflation is down; Congress is struggling to get the budget deficits under control; but the interest rates remain at murderous levels. How come?

Brown cited the figures. From 1969 to 1979, the gap between the prime interest rate and the basic inflation rate averaged 1.96 percent. In 1981, it widened to 9.77 percent. In the first quarter of 1982, it was 13 percent. How come?

Volcker said the real reason was that severe and prolonged inflation from 1966 through 1980 left the money markets scarred and wary. He predicted that interest rates would ease -- how much or when he would not guess -- and hinted that the Fed itself might relax a bit on its money controls, as some analysts think it is already attempting to do.

But he demurred at mp calls "a moment of truth" for both Reagan and Volcker. any changes that would curb the independence of the Fed or force it to abandon the basic policy it adopted in 1979.

That is not likely to be the last word on the subject. On July 1, the next installment of the tax cut goes into effect. The same day, the Fed's Open Market Committee meets to review its money supply goals for the remainder of the year.

More and more politicians are concluding -- rightly or wrongly -- that the little-understood October 1979 decision holds the key to the interest squeeze, that the "Carter recession" of 1980 and the "Reagan recession" of 1981-82 were both the result of what Heckler called "Volckernomics." They are demanding that Volcker and Co. come up with a monetary policy that brings interest rates down and permits the recovery to take place.

That kind of pressure is building fast, hastening what Kemp calls "a moment of truth" for both Reagan and Volcker.