Last Tuesday morning, as the space shuttle Columbia was preparing to reenter the earth's atmosphere, there appeared in this space a report of a critical letter I had received.

The writer said he was opposed to spending money on space research at a time when we are cutting back on social programs aimed at alleviating human suffering. He called Columbia's flight "a joyride to nowhere."

I disagreed with this view, but apparently with insufficient vigor to suit some readers.

Catherine S. Kozlowski of Burke, who is a computer software systems analyst wrote: "Today's column in which a reader referred to our space program as a waste of money simply cannot go unanswered.

"The men and women of NASA who have made our space program the unqualified success it is are scientists and engineers, not politicans or public relations experts. For this reason, the general public has little or no knowledge of the hundreds of ways the space program has benefited our society.

"The semiconductor and computer industries which contribute hundreds of millions of dollars to the national economy each year and employ hundreds of thousands of workers owe their present preeminence to technologies developed in the space program. Everybody who owns a digital watch, a pocket calculator or even a programmable, energy-saving thermostat, has been touched by the space program.

"Materials developed for the space program penetrate every aspect of our lives, particularly in the field of medicine, where plastics developed for the space program are being used for artificial limbs, replacement hip sockets and even artificial heart valves. Please, Mr. Gold, in the future when somebody calls our space program a waste of money, set them straight."

This column is being written by by a man who is in his fourth year of being well served by one of those plastic heart valves. I don't need to be persuaded that science and research are of great value to us, whether we pursue our quest for knowledge on earth or in the heavens.

Charles F. Withington also responded to NASA's critic. He wrote: "The letter said that NASA's 'joyride to nowhere' was a waste of money and 'we do not have enough money to care for the ill, the elderly, the poor or the hungry.'

"I would like to point out that the United States Agency for International Development is using the results of NASA's 'joyride' in helping the poor and the hungry in less developed countries of the world.

"We are trying to alleviate human suffering by training third-world decision-makers in the techniques of analyzing satellite pictures and images to determine their natural resources.

"At the present time, the data being used are supplied by NASA's Landsat satellite, and we are eagerly awaiting the pictures that will come from the space shuttle flights. Without satellite imagery, it would be much more difficult for us to determine the extent and yield of crops, the spread of deserts, the depletion of tropical soils and forests and the condition of range lands. It would also be more difficult to locate underground water and mineral deposits. We have a long way to go before we can wipe out hunger, but NASA's 'joyrides' are helping us to toward that goal."

My plastic valve begins to thump ominously when people criticize the attempts of scientists to understand the world in which we live, so please don't send me any more anti-NASA letters. I think I'm much too young to die.

It I can't appeal to you on humanitarian grounds, think of it this way: My demise would have an adverse monetary impact on so many physicians, surgeons, nurses, laboratory technicians, hospitals and pill makers that the ripple effect could be a serious blow to the national economy. POSTSCRIPT

Bob Orben hasn't gone into orbit yet. He's still learning to live with ordinary airplanes, but says he doesn't understand the terminology -- "economy class, " for example. In Orben's opinion, "There is very little economy and even less class."

Getting booked on a flight is also a problem, and Orben says little has changed in the last 78 years. "For instance, on that very first flight back in 1903, Orville Wright got a seat -- and Wilbur was on standby."