SEEKING MY Christian duty, I reached for the lemon pie and then (this was the great stroke) made Cynthia Hoover take the large coconut cake instead of sharing a piece with Helen Hollis.

Cynthia ("Harpsichords and Clavichords" if you read the Smithsonian publications, as you should) Hoover has every virtue, I believe, except the cardinal one of ordering one's own dessert (martini, egg roll, Caesar salad, fortune cookies, etc.).

Hollis ("The musical Instruments of Joseph Haydn," and "pianos in the Smithsonian Institution") had given up the idea of dessert since nobody else wanted any at first.

"But we'd delighted to sit here and watch you eat a tremendous pastry," I had said to make her feel comfortable, but she said no, it really was not important.

And then out of nowhere, Heaven maybe, came a waitress with a tray of sin.It was into this breach that I leapt, taking the pie and seeing that nobody nibbled on anybody else's dessert (a thing that can cause harder feelings than some people know) and thus insured a work day of harmony in the section on ancient instruments, in the National Museum of Technology's Division of Musical Instruments.

It was the least I could do, after all, for all this section of the Smithsonian had done for me.

Nobody knows why this marvelous part of the Smithsonian is relatively little known, since it is one of the world's preeminent collections, with 2,000 items in it.

Hardly anybody seems to know at 11 every morning on Tuesday through Friday they demonstrate their 18th century and other amazing instruments at the museum. This past Wednesday, for example, Mary Price, violinist, demonstrated the viola da gamba which goes "woo" like a cello but has (I thought) a softer sound, though sharper-edged.

The viola d'amore, which is more like a violin, has seven strings plus a separate set of seven strings beneath them, to vibrate in sympathy. Its sound is blessed with an aureole, so to speak, from the sympathetic strings, and this is sad and sexy.

An American contribution is the phonoviolin, a horrendous animal with a trumpet like His Master's Voice that blares the string sound to anybody that will listen.

Some of the strange violin noise you have heard on early 20th-century records may well have sprung from the phonoviolin.

Hollis said it is wonderful the way people respond to these rare instruments. She played a bit on the glorious Steinway that Paderewski used for 75 concerts and on a little piano of the sort Mozart used in Vienna (the least touch of the key and it sounds) and some of the other fabulous harpsichords with their sound boards painted with roses, daffodils, anemones, carnations and imagination.

Once she was demonstrating the virginals, a small keyboard instrument set on a table and much favored by women, not necessarily virgins, in past centuries.

"Oh, that was marvelous," cried a flower-child-type young man, attending with a glaze of his fellows. "If there's time, would you play some more in the vaginals?"

In the conversation laboratory, which I would have called the repair shop, there were 20 keyboards neatly shrouded with clear plastic cloths, in stages of restoration.

Quills from crows used to be used as plectra for harpsichords, but now plastic serves, and it probably stands up better. Somewhere, probably, somebody is complaining that God meant harpsichords to have crow quills, but then there's one in every crowd.

In recent days this already astounding collection has been augmented by four stringed instruments (one a Stradivarius violin with some unusual features in the purfling, and a mindboggling collection of 14 violins lent anonymously and worth seven trillion dollars (the Smithsonian primly declines to discuss market prices so I'll just blurt it out).

These are "on loan" but I hope forever.

Last weekend 92 people from around the country came for one of Connie Mellen's brainstorms. About eight years ago she thought why not a weekend in which hotel arrangments, food, a few nice parties, etc., were all taken care of, so people could concentrate on hearing music on these old instruments. The idea has been an increasing success. The charge is less than $300 for the works, but even so the weekend produced $12,000 profit for the The Friends of Music.

This is a rather small group, as Helen Smith was telling me, supports both with money and with volunteer energy the concerts, recordings, publications, workshops, etc., of the Division.

Joshua Taylor lent his National Collection of Fine Arts museum for the weekend subscribers' banquet.

Hardly anybody in the capital ever had the privilege, but the weekenders from 17 states had cocktails in the room where Lincoln's second Inaugural Ball was held, and had dinner in the Granite Hall. They attended an opera, were entertained at a Turkish Embassy reception (one of the town's grander sort of embassy) and took a boat ride on the Potomac, and this sort of thing went on and on around the clock.

There was an evening concert at the museum in a small elegant room with an enormous Waterford chandelier with 46 candles (as I unreliably counted) that scalded nobody with hot wax. (Before they used to drip on people.)

Musicians of the orchestra came from all over - my wife and I took a horn player and his wife back to their hotel, and they were from New Hampshire. Others were from Detroit, Chicago, New york, all paid a very modest sum to come to Washington.

At a reception following in the Presidential Room, you could meet all the musicians over wine and crunchables. Tom Wolfe built the copy of an old harpsichord that blended so well with the great Dulcken harpsichord played by James Weaver that is was hard to tell them apart, though the 18th century one is a bit more agressive in tone.

This is not the place to say that a city can hardly call itself a capital if nobody can get any form of transportation from one of its major museums after a Saturday night concert. Cab service is disgusting.

You might think a city government would give some sort of damn how people know get around in it, but as everybody knows except the government you can't get a cab, bus, subway or horse from the bulk of the city to any other place in the city for half the hours of the day - all this while idiots prate of saving gas.

But peace. Assuming everybody got home Saturday, they wound up with breakfast Sunday at the Renwick Gallery.

I never went anywhere in this city or did anything in it that seemed to me a greater privilege than attending parts of this weekend, and nothing is a better bargain though I went free but all the Steering Committee volunteers pay full price, in addition to arranging all the details without any salary of fee).

So when I reached for the lemon pie, after the concert and receptions and demonstrations and confabs with the staff, it was not only my duty (for otherwise Holllis would have wavered and had no dessert) but my sacrificials way of saying thanks.