He sits at a cubicle in a converted language lab, wired to it by earplugs, hunched over a slowly revolving tape reel.

A song begins. "Lucille." Kenny Rogers' oddly broken voice. After six bars the man jots down three names: composer, lyricist and publisher.

Fast Forward to a soap jingle. Five bars. He writes down the credits.

Fast Forward to the theme song of the radio show. Eight bars, a tough one. But he identifies it, writes it down.

Fast Forward . . .

An ASCAP music monitor has to be a very special kind of person. You have to known a lot of a music, from country to classical. And you have to not mind never hearing a song all the way through.

In fact you get a bonus for plowing through more tape than normal. Some veterans cover 12 hours of tape in a single shift. There are 33 radio monitors and five for TV, working two shifts at the Lincoln Plaza offices of the American Society of Composers, Authors and Publishers. They keep busy. Every year they sample 60,000 hours of local radio and 30,000 hours of local TV.

What's happening here?

The best way to understand is to put yourself in ASCAP's place: How do you pay royalties to song writers and others involved in copyrighted musical work?

For a book it's simple: you just add up the number of copies sold and take your cut. But songs? Do you realize there are 7,000 local radio stations in the country? And every one of them has its squad of deejays who spin records by the dozen, not to mention the theme songs and background music and advertising ditties and bridges.

Then there are the 700 TV stations in America, then three TV networks, and Muzak-type wired stuff played in supermarkets, and symphony concerts, and music played in restaurants, bars, hotels, night clubs, theme parks and skating rinks, and what have we left out?

Now, the networks, send ASCAP their program logs listing every crumb of music played. So do the wired-music people and the concert promoters.

But that still leaves a bit of a gap, Americans hear about 2 billion musical performances a year, live and recorded. How can you possibly listen to it all so you can pay the royalties owed?

You can't.

There are two basic ways to approach the problem. One is to try to get all those music sources to log the songs they pay. This is the method used by Broadcast Music Inc., ASCAP's chief rival. The other is ASCAP's way: a statistical sampling worked out by an independent firm and weighted to match the size of payments made by the sources.

For instance, radio stations pay 1.7 per cent of their ad income to ASCAP in license fees. It follows that a [WORD ILLEGIBLE] paying $20,000 a year will be sampl [WORD ILLEGIBLE] more than one paying $2,000.

By the same taken, royalty on a given song performance can [WORD ILLEGIBLE] a dime to $500 or more.

Naturally, with 7,000 stations and [WORD ILLEGIBLE] 760 hours in the year. 60,000 hours of sampling will be bound to miss a lot of songs. The BMI system is more complete. But ASCAP maintains that it pays more for what it does catch. A standard suggestion for beginning songwriters is that they move to ASCAP when they hit the big markets.

Meanwhile, our monitor has run into a snag. He's found a song he doesn't know. He plugs in some of his colleagues, but they don't recognize it either. If it had lyrics, he could try the first-line lile, but it's just a bunch of notes. What is it? How to find out. Call up Lawrence Welk and hum it over the phone?

No, the monitor just writes down the opening bars in solfeggio, do-me-fa-sol, etc, and goes to the solfeggio file, a huge bank of index cards indentifying thousands and thousands of melodies in the language of do-re-mi. If he still doesn't find the song he logs iometimes riding on these strictly random samplings of radio and TV stations, the system needs a lot of checking. Ken Ayden, a former big-band trombonist who runs the listening operation, would led pictures be taken of his staff [WORD ILLEGIBLE] someone try to tamper with them. Sport checks also are made of the logs supplied by networks.

There is no end to the ingenuity of some musical scamps. A while back some network music directors tooks to writing their own musical bridges for certain big shows. Though these were merely a few grant chords, they came in for royalties, and the royalties were big because network TV is big.

"Some of these guys were getting paid more than Irving Berlin," and Walter Wager, ASCAP public relations director.

There are also the nightsports that object to paying license fees as well as musicians. These sinners usually are caught by roving auditors, undercover operators or complaints from rival club.

There are lawsuits too. ASCAP has about 400 a year, settles most of them.

"We have a new problem today," Wager said, "In the 30s a song had a shelf little of about three months. Now it gets played for maybe eight weeks.

If it's a hit, the Top 40 stations run it into the ground so you never want to hear it again. Well, it's possible to have a fairly big song that is played dozens of times over a few weeks and then dies out - and is never picked up by our samplings."

To counteract this, the ASCAP board, which is elected form the membership and thus is more sensitives than many boards, set up a system of diminishing returns, cutting the take of top moneymakers and spreading it among the others.

This flow-down plan complicates even further the intricate division of the $94 million that the agency takes in yearly.

(ASCAP has always been alert to the feelings of its members. At the inaugural banquet in 1914, founders Victor Herbert, Jerome Kern and others had to decided what dinner music to play. That's like who'll say grace at a banquet of bishops. Their solution: play nothing but the Blue Danube waltz, over and over, all evening long.)

The monitor is laughing in his earphones. He tunes in a young woman, and she laughs, too - monitors come in all ages, sizes and colors, and the test they have to pass before they can even apprentice would stop a passel of music critics - but she's never heard it either.

He writes down the words and music to be checked by another department, the backstoppers who fill in names of publishers and any details the monitors missed.

Now he puts the tune on his speaker for Ayden's benefit. No title is given. (Some deejays consider it chic to leave out the title, a fact that makes a monitor's stomach clench.) The tune jogs along with the relentless rhythm of a gumehewer. A young man is singing.

" ... Rhonda ... on my Honda ..."

The monitor shakes his head and returns to his headset. It is barely lunch time and he still has a reel to go.