They think they can count on Republicans in Congress who say that the 1933 Glass-Steagall Act is a Depression-era relic. Fears that a market collapse could affect banks are old hat, these descendants of Dr. Pangloss insist. Break down the fire wall and let the Federal Reserve keep a benign eye on everything financial; we don't even have to fear fear itself.

Not so fast. Suppose the Big Quake afflicts California. Or maybe a Category 5 hurricane, which comes every decade or so, rips along the expensive expanses of a place like Long Island. That would put a lot of pressure on even the most reinsured insurance company.

If you heard such news, and you could switch your money out of the bank affiliated with that insurer with a keyboard stroke, wouldn't you be inclined to play it safe? And wouldn't that Internetted panic cause a run on the superbank?

That's being alarmist, of course. Such disasters are just as unlikely as a market crash (which we all assure each other can never happen again). But before the cash cow of Chase Manhattan starts making cow-eyes at the thundering herd of bulls of Merrill Lynch, Congress had better take a close look at the downside of upsizing across the old boundaries.

1. No private enterprise should be allowed to think of itself as ''too big to fail.'' Federal deposit insurance, protecting a bank's depositors, should not become a subsidy protecting the risks taken by non-banking affiliates. If a huge ''group'' runs into trouble, it should take the bank down with it; no taxpayer bailouts should allow executives or stockholders to relax.