THE NEW SENATOR from Missouri, John C. Danforth, got it just right the other day when he told the chairman of the telephone company, "Show me." The chairman, John D. deButts, was claiming that residential telephone rates are now subsidized by long distance service. But the Federal Communications Commission says it has seen no evidence of such a subsidy, and AT&T hasn't kept its books in the past in a way that reveals one. So Sen. Danforth, quite properly, told Mr. deButts that the "burden of proof" is on the telephone company to justify its claim.

The subsidy is central to AT&T's persistent campaign for legislation cutting off competition in the telecommunications field. It has built a massive lobbying effort around the idea that more competition will mean poorer service and higher rates for residential customers. The FCC and the Department of Justice, which have been promoting competition, insist that neither result is inevitable. And no one appears to have the economic data to back up the assertions.

That lack of data has not deterred AT&T's efforts on Capitol Hill, however. Mr. deButts asked last week for an immediate prohibition against new competition for his company while Congress studies the whole telecommunications field. And the "Bell Bill," as a piece of legislation entitled "the Consumer Communications Reform Act" has become known, is still being pushed vigorously from all over the country. The force of that effort should not be underestimated. The Bell system reaches into 48 states and employes a million people. It should have been no surprise that its pet legislative proposal picked up more than a third of the members of Congress as sponsors when it was first introuduced last year.

That bill, which would grant AT&T an effective monopoly in its industry, does raise many complex issues. The telecommunications field is changing rapidly and its future is not yet defined. As computers become tied to communications circuits, a whole new kind of daily life begins to unfold. It is not clear, at least to us, what form this exploding industry should take or what role government should have in it or in its regulation. But it is clear that no one company ought to have a stranglehold on it and on the introduction of new equipment and new techniques. That is why Congress should proceed with all deliberate speed in dealing with the questions opened up by the Bell Bill and why Sen. Danforth has the right approach.