I frankly did not want to write this letter. I'm involved in a Christian ministry, have no interest in politics and realize that anything I say about Bob Woodward will be immediately suspect because we were once adversaries.

I've written the letter, however, because I simply could not ignore the situation.

In the Saturday, Sept. 26 edition, The Post reported excerpts from Bob Woodward's book "Veil: The Secret Wars of the CIA." The article describes Bob Woodward's last conversation with Bill Casey in Mr. Casey's room at Georgetown University Hospital several weeks after Mr. Casey had undergone surgery for a brain tumor. According to the article, Mr. Casey acknowledged approving the diversion of profits from the Iran arms sales to the Nicaraguan contras. When Mr. Woodward asked why, Mr. Casey said, "I believed."

Coincidentally, I underwent major surgery and was a patient at the Georgetown Hospital during the entire month of January. I occupied the room immediately below Bill Casey's. Without wishing to impugn anyone's veracity I feel compelled because of my personal experience in the hospital to comment on The Post article.

One evening, a hospital official visited my room. He mentioned in passing that Bob Woodward, under false pretenses, had attempted to enter Mr. Casey's room but that he had been turned away by security personnel. These personnel, by the way, had maintained a 24-hour vigil in front of Mr. Casey's door since his operation. Hospital officials were less than pleased with Mr. Woodward's attempt to invade the privacy of a man who was gravely ill.

In the latter part of January -- it was either the 26th or 27th -- I was invited by Mrs. Casey to visit Bill since we had been associates in the Nixon administration. I did so; it was for me a very moving experience to be able to offer spiritual counsel and pray with an old friend. He was unable, however, to communicate other than by squeezing my hand and making grunting sounds that were unintelligible.

Mr. Casey unfortunately cannot respond himself to the charges made in The Post article or the Woodward book, so I feel an obligation to write. Mr. Casey was physically unable to make the statement alleged, even if Mr. Woodward had gained access to his room. As I am sure hospital officials would attest, the meeting described in the article could not have taken place. CHARLES W. COLSON Washington