The way I figure it, I have opened approximately 60,000 envelopes in my seven years of fund-raising on behalf of Children's Hospital. After that much slashing with a letter opener, and that much letter-reading, you'd think my heart would have grown barnacles.

But every year, I get letters that touch the soul -- and that cut through any defense that any barnacle could erect.

Here are three soul-touchers that arrived in recent days. I defy you to read these and maintain that the world is a rotten place.

First Barnacle Beater: Mary Branch.

"Enclosed is my check for $24 in honor of my third-graders at Terra Centre Elementary School in Burke, Va. ($1 for each child)," Mary writes.

"Bob, I enjoy sending you a check each year. They enjoy the attention in your Post column!"

And I enjoy the spectacle of a teacher who spends 24 of her precious dollars not to escape her students (she'd be forgiven for wanting to) but to salute them.

I don't know about you, but that's the kind of teacher we all hope to have for our kids, and so seldom find. Thank you, Mary, and the same to Your 24. A little ink for them is the least I can do when they've got a teacher like you.

Second Barnacle Beater: Luisa Giorla of Rockville.

"I am a waitress at Cafe La Rouche in White Flint Mall. A strange thing happened to me last Saturday, Dec. 19," Luisa writes.

"I waited on a middle-aged man who ordered a small meal and his check came to $11. He paid me with a $100 bill.

"When he left the restaurant, I noticed a $20 bill, a $10 bill, a $5 bill and some ones still sitting on the table. So I ran out of the restaurant to give him his change that he had forgotten.

"He said, 'No, it's yours. Merry Christmas.' He had left me a $40 tip on an $11 check.

"I probably wouldn't recognize this man if I ever saw him again, but I can't express my thanks to him enough. And I thank God that there are still people in this world who know that the real meaning of Christmas is giving.

"I'd like this man to know that his money is being put to better use than simply to indulge the extravagances of a 19-year-old waitress."

Luisa's $40 check was right beneath her letter. Which makes two people in White Flint Mall on Dec. 19 who know the real meaning of Christmas.

Third Barnacle Beater: Paul Valcheff III of Arlington.

"Like many other 26-year-old single people, my Friday evenings are usually spent enjoying Happy Hours with friends and friends-to-be," Paul writes.

"Needless to say, the topic of children rarely comes up. But after reading your column today, about the soon-to-be mother, I figure a small investment now might pay big dividends in the future.

"So instead of going to Happy Hours tonight, I'm sending you the money I would have spent anyway {$20}. Maybe a less fortunate child can benefit from the great work being done at Children's Hospital. Staying safely at home for one night is a small sacrifice compared to the rewards that Children's Hospital provides."

I sincerely hope that other single people hear your message, Paul -- and heed it.

I also hope that non-single and non-young people will recognize the hiss of air escaping from a cliche that has just been punctured.

Not every single 26-year-old man is without a conscience, or a sense of responsibility. Many thanks to Paul, who knows that the happiest happy hour arrives when you help others.

A word to those of you who itemize deductions on your income taxes:

Because this is the last day of 1987, it's the last day you can make a contribution to our annual Children's Hospital campaign and claim it on your 1987 tax returns.

I'm sure that many of you have checking accounts that have been turned into swiss cheese by Christmas. I'm just as sure that many of you have savings accounts that look as if they've been splattered with disappearing ink.

But you can recover from the doldrums if you obtain a hefty tax refund. So why not take a giant step in that direction?

Make a gift to our campaign, and make it today. Uncle Sam will underwrite it, and several hundred sick kids will deeply appreciate it.

Will you group givers ever quit? I hope not! Here are the latest group contributions to arrive in the mail:

T.G.I.F. II Ladies Bowling Group ($41).

Employes, Personal Property Management Division, United States Department of Agriculture ($25).

The Republican National Committee staff ($397.65 in memory of Eleanor Manuel).

231st Combat Communications Squadron, D.C. Air National Guard ($3,000 in pledges to support the journey of Lt. Gregory Bates and Lt. Pat Harris, who biked from Gulfport, Miss., to Andrews Air Force Base last summer).

Zeta Psi Chapter of Beta Sigma Phi ($30).

Front office clerks at Potomac Electric Power Company's Potomac River Generating Station ($60 in lieu of a gift exchange).

BNA Communications Inc. employes, Rockville ($125, with a special welcome-aboard to these first-time donors).

O'Brien Home Improvement, Rockville ($150).

The Calligraphers Guild of Washington ($25).

Oakcrest Towers Funsters Senior Citizens Club, Forestville ($110 collected at the Christmas party).

Arlington Post 139, The American Legion ($50).

Officers and staff at Aronson, Fetridge, Weigle & Stern, Bethesda (a superb $5,600).

The Uptown Office, Shannon & Luchs ($258).

Staff, Dental and Medical Materials Group, Polymers Division, National Bureau of Standards, combined with employes of the Paffenberger Research Center of the American Dental Association Health Foundation ($253 in lieu of Christmas cards).

Employes of the National Council of Farmer Cooperatives, American Institute of Cooperation, The Farm Credit Council, Agricultural Cooperative Development International and Volunteers in Overseas Cooperative Development ($222.55).

The staff, Office of Chief Counsel, Food and Drug Administration ($171).

Employes of Grady Management Inc., Silver Spring ($404).

Students in grades 7-12 at Edmund Burke School, Northwest ($60, with special thanks to chief collector Christopher Dyer).

Employes, Board of Veterans Appeals, Veterans Administration ($351.75).

United States Senate Staff Club ($150).

Corporate Visions Inc. of Northwest ($2,000).

The Third Wednesday Bridge Club of Gaithersburg ($20).

The Prime-Timers of the Towers ($190).

"Eighteen Who Care" from the Farmers Home Administration, U.S. Department of Agriculture ($217).

Nova Delivery Inc. of Vienna ($1,000).

Knights of St. John's Ladies Auxiliary 310, Suitland ($50).

Association of American Foreign Service Women ($1,500).

A fine showing! Thanks to all of you. TO CONTRIBUTE TO THE CAMPAIGN:

Make a check or money order payable to Children's Hospital and mail it to Bob Levey, The Washington Post, Washington, D.C., 20071.