It is difficult to think of a president who has made as many remarkable impromptu comments as Ronald Reagan. Lou Cannon has chronicled many of them, and another was noted in wonder recently by The New York Times, which picked it up from The Washington Times.

"Remember," the president said, "there once was a Congress in which they had a committee that would investigate even one of their own members if it was believed that that person had communist involvement or communist leanings. Well, they've done away with those committees. That shows the success of what the Soviets were able to do in this country with making it unfashionable to be anticommunist."

The president's nostalgia for the good old days of Martin Dies, J. Parnell Thomas, Richard Ichord and the tireless Joe McCarthy sent me to a book. I sometimes bring it along for show-and-tell discussions of the First Amendment at high schools. The book was given to me by Fred Bass, owner of the Strand Book Store, the largest source of secondhand books in New York and maybe anywhere else. He often buys private libraries, and this book came from one of them.

The book is bound in red, but there is no visible author's name or publisher on the spine. Those areas are covered with tape. The only type on the cover of the book is The Civil War. Everything else is also covered with tape. The reason for all this caution becomes clear when the book is opened to the title page:

"The Civil War in the United States" by Karl Marx and Friedrich Engels.

Fred Bass tells me there were other books in the man's library whose authors were also hidden. At some point in the heyday of those committees mourned by the president, the collector had decided to take precautions in case an informer came into his home.

The school kids gape at the book, it being a more intriguing reference to those years than the cursory mentions of Red Hunts -- when there are any references at all -- in their social studies textbooks. I also tell them, out of my own memories, of people during those years who were afraid of signing any petitions for anything at all.

Judy Holliday, the actress, was somewhat bolder. After having been hauled before a committee to explain her act of conspiracy in supporting Henry Wallace in 1948, she said, "I don't say 'yes' to anything now except cancer, polio and cerebral palsy."

Accounts of those committees puzzle high school students these days. This kind of fear is unknown to them, and they are curious to find out what happened back then to frighten people so.

They ask if I ever had to testify before one of those committees. No, but in 1970, without asking me a word, the House Internal Security Committee (a successor to the House Un-American Activities Committee) placed me on a list. The staff had put together the names of speakers who, they said, appeared at college campuses around the country "promoting violence and encouraging the destruction of our system of government."

The committee's list appeared, among other places, in The New York Times. Alongside my name were three organizations. According to the Internal Security Committee, I belonged to each one. Just like the committee, The New York Times did not ask me whether that was true. Actually, I belonged to none of them, and never had.

As for my promotion of violence, years ago A. J. Muste had convinced me of the saving logic of nonviolence. During the period covered by the list, at a college where I had been invited to speak against the war in Vietnam, I was shouted down for also condemning the use of violence against those supporting the war in Vietnam.

For some years afterward, I would meet people who said they had been surprised to find out that I belonged to the three groups cited in the list of itinerant firebrands.After all, if a congressional committee said so, withfurther imprimatur of The New York Times, it must all be true.

I can't tell the school kids I ever suffered any real injury because of the committees whose demise the president regrets -- though a considerable number of people suffered a great deal, and a few committed suicide. Still, the nation survived the committees.

The Bill of Rights is marvelously resilient, being able to keep on keeping on, even under a president who hasn't the faintest idea that it was not the Russians who stealthily managed to kill those un-American activities committees. It was us.

And contrary to the president, the result was not to make anticommunism unfashionable. It was, I tell the kids, to make the differences between the two systems clear again. Another reason why the history of those committees ought to be taught in some detail in all our schools.