In the wake of last month's stock market collapse, Rep. Tony Coelho, majority whip, circulated a ''Dear Colleague'' letter discussing how the affirmative action taken by the Roose-velt administration in its historic ''First 100 Days'' not only resuscitated the U.S. economy in 1933 but has saved our collective bacon in 1987. In this, Rep. Coelho has a point. Without the safety and soundness net woven around the nation's banking and securities industries by President Roosevelt and his successors, history might have repeated itself.

It was right in 1933 for a Glass-Steagall wall to be constructed between the banking and securities industries. It is bad in 1987 to keep an impermeable wall in place. Those who advocate competitive equality for the financial services industry do not support a return to the wholesale free-for-all that led to the market's collapse in 1929. Rather, they would like to penetrate the Glass-Steagall wall to strengthen financial institutions' ability to compete effectively, while enhancing existing statutory and regulatory safeguards and strengthening a supervisory net that will prevent the conflicts of interest and insider abuse of the 1920s.

As a former chief counsel to the Office of the Comptroller of the Currency, I find these efforts wholly laudable. However, there is a danger if the skeins of that net are not loosened or, indeed, are pulled even tighter. What Rep. Coelho does not take into account when weighing the events of 1929 against those of 1987 is that, according to Plutarch, ''it is circumstance and proper measure that give an action its character, and make it either good or bad.''

A ''proper measure'' needs to be struck by Congress in 1987's circumstances. Clearly, a return to the draconian days of 1933 would be self-defeating, not only for the players in the financial arena but for our economy as well. BRIAN W. SMITH Washington