ON THE OPPOSITE page today, Interior Secretary Cecil D. Andrus takes issue with our editorial on Georges Bank, the unique natural fishery in the Atlantic. In it, we argued that it was a bad idea to lease part of Georges Bank for oil production. Nothing in Secretary Andrus' reply persuades us that this is not so.

There is, first, the seemingly straightforward question of the value of the Georges Bank fishery. Is it less than $200 million, as Mr. Andrus claims -- as distinct from the $1 billion figure we used? International commissions, private industry and different agencies within the government all cite very different numbers. The Post chose a middle value. One could go, for example, to Interior's own Environmental Impact Statement and find, on page 113, that the annual catch on Georges Bank amounts to 500,000 metric tons, or 1.1 billion pounds. Using a conservative value of 40 cents per pound of fish, and multiplying by the economic multiplier of 4.24 (again, this is Interior's recommended number) would give a total annual value to the United States of $1.8 billion.

More important than arguments over uncertain statistics, however, is the crucial difference -- which Mr. Andrus seems to have missed -- between a finite and a renewable resource. He says that to note, as we did, that the estimated oil reserve would provide only the equivalent of eight days of current consumption is no more to the point than it would be to note that all the fish in the Georges Bank would give only four meals' worth of protein for every American. But energy can be pumped out, used once and is gone. A fishery renews itself each year.

Then there is Mr. Andrus' assertion that "studies to date indicate no long-term ecological damage" resulting from offshore drilling. If anything, the evidence points the other way. The longest study of the after-effects of an oil spill is being carried out at Falmouth, Mass., where a spill occurred in 1969. In Falmouth, the shellfish beds are still closed and there is continuing evidence of oil damage. Most independent, responsible scientists argue that the best that can be said is that it is simply not known yet what the long-term effects of marine oil pollution will be. Prudence dictates that the experiments not be carried out in what all agree is the world's most productive fishery.

At the very least, a deep concern for the fishery would argue for two key changes in the lease sale conditions. As is often done, the leases should allow only exploration, rather than exploration and production. Then, when the size of the oil resource is no longer only an estimate, the nation can accurately judge the relative importance of these two resources. The lease sale should also require that the "best available" technology be used -- this requirement is now strangely absent. We suspect that is because there would be little industry interest in exploring Georges Bank if it were imposed: the field is simply too small to justify the expense.

The wisest course, however, would be to postpone development of Georges Bank indefinitely, or at least until -- and we doubt it would ever happen -- this relatively small oil field became vital to the nation's energy balance. The oil won't disappear; the fish might.