Your recent letters include several themes with a common denominator - memory.

Memory plays tricks on all of us. Writers learn not to depend on memory because a writer's goofs live on forever. People save clippings of even minor errors: major blunders are preserved in anthologies and become part of city room legends.

A few days ago. I compared the tenfold increase in the price of coffee to the tenfold increase in wages that occurred during the same span of years.An Alexandria man wrote: "Five years ago, I paid about 42 cents a gallon for regular gas. Now I pay 65 cents, an increase of less than 55 percent. My salary has risen 106 percent in the same period, so I suppose I'm better off, but sometimes it doesn't seem so."

Of course. Taxes are higher now. And many prices have risen faster than gas prices. Also, consider this.

A picture in the official magazine of the Washington/Maryland Service Station Association shows a 1973 price sign near some gas pumps. The price on regular gas was 29.9 cents a gallon, not 42 cents. So if my correspondent is now paying 65 cents, his price for gasoline has more than doubled, just as his salary has. Only his memory has retrogressed.

Discussion of the corporate names of Metro's predecessors moved Marvin A. Marx of Silver Spring to recall that around 1930 the fare on Connecticut Avenue buses ("some of them double-deckers") was 6 cents cash, eight tokens for 40 cents. My recollection is that by 1945 tokens were three for a quarter. When fares were raised again, tokens were temporarily eliminated, and leftovers were redeemed for cash. Many readers sent their tokens to me for Children's Hospital, and we redeemed tens of thousands of them.

Although last Thursday's column answered a pending question about the Civilian Conservation Corps camps, I was wrong in assuming that this would end the matter. Letters about the CCC continue to arrive in surprising volume, and many contain interesting comments and recollections. Polly Sayers, for example, remembered that she met her husband during those days. They used to listen to WLW's "Moon River" program each night, and that raised a question about the program's theme music. Inasmuch as the song "Moon River" wasn't written until years later, what was the theme music used on that program in the 1930s?

As I recall, it was a caprice written by Fritz Kreisler, possibly under a pseudonym. Some of the words used with Kreisler's music still seem to stick in my mind: "Moon River, a lazy stream of dreams where vain desires forget themselves in the loveliness of sleep . . . Moon River, enchanted white ribbon twined in the hair of night, where nothing is but sleep . . . Drift on, dream on, Moon River, to the sea." At least three readers will no doubt tell me that my memory is faulty - and send me three different corrections.

Lawyer Louis Alexander Traxed remembers the COC camps and confirms that each enrollee received $25 a month for his parents and $5 a month for himself. He explains that $5 was enough because each young man also received "free bed, board, clothing, medical care, transportation and recreational equipment."

Food was plentiful and cheap. "The value of the individual raton varied from 27 to 33 cents a day, from which we saved enough money to have chicken every Sunday. The boys killed and dressed the chickens. Sides of beef averaged 8 and 10 cents a pound, liver 2 cents, oranges $1.88 a crate.

"Each enrollee could take all he wanted, but had to eat all he took - or go on KP."

L. Corbett, "USA Ret," wrote under a Washington postmark to challenge our Labor Department official's recollection that COC wages of $30 a month were "the same pay an Army private received in those days." Corbett said:

"An Army private was paid the magnificent sum of $21 a month, out of which he had to provide clothes, cleaning, laundry, etc.

"The Army supervised the start of CCC. Later it was operated by Reserve officers. The difference in pay was a sore point with Army personnel. Army pay was not raised until the one-year draft, just before World War 2."

As I was reading Corbett's letter, colleague Jack Eisen popped into my office, so I handed him the letter. "You went into the Army about a year before World War II." I said. "What was your pay?" Jack read the letter and said, "I think he's right. A PFC got $30. I think, but I know my pay was $21." Even a memory dimmed by passing time can't obscure that kind of wage.