Isaac Stern had reached the finale of the Tchaikovsky Violin Concerto when suddenly, at the peak of a fast-rising passage, he stopped.

Stamping his foot several times, the reowned violinist, standing on a specially built platform in the Kennedy Center Concert Hall, swore in some unintelligible language and then broke into clear English:

"How could the hair on my bow break like that? It got all wrapped around my finger!"

By that time yesterday afternoon, Stern and the members of the National Symphony Orchestra had been working for nearly six hours to record the concerto for Columbia Records. Under the direction of Mstislav Rostropovich, Stern and the orchestra had been rousing up great quantities of enthusiasm with the concerto at this week's NSO concerts.

Yesterday's session was a historic breakthrough for the orchestra. It marked the first time that all recording costs were paid for by the recording company. In the past, individuals or members of the board of directors have paid these very substanial amounts.

This new move advances the orchestra another step into the big league occupied by the orchestras of Boston, Cleveland, Chicago, New York and Philadelphia.

For Rostropovich, an artisr whose name has already appeared on hundreds of recordings, both as a cellist and conductor, the session also had special meaning. It is his first recording as a conductor in this country.

The National Symphony made nine recordings under Antal Docati's baton during his seven years as music director. Several of them won major international prizes. He included music by Wagner. Tchaikovsky, Debussy, Messiaen, Gerhard and Robert Russell Bennett in those recordings.

Every 60 minutes during the recording session, the players stopped for a break, during which Stern and Rostropovich moved into the control room to listen to the results. After one visit, Rostropovich returned to the stage and exhorted his musicians;

"More feeling make!"

Columbia producers and engineers had turned the orchestra's offstage green room into their control center for the day filling it with banks of consoles for the 16-track recording system dual turntables and all the other parapheranalia that goes into today's stereo recording.

In this room. Stern was listening intently when along came an especially luscious passage on which he had lavished some highly romantic phrasing. With a big grin, he said, "We can fry chicken for the next 10 years on that fat!"

The music began at 9 in the morning, broke for an hour at noon, and continued into overetime, not ending until about 4:40 in the afternoon. Each player in the orchestra will receive about $250 for the regular sessions, plus a bonus for the overtime.

Next week they will have another full day of recording under the baton of Leonard Bernstein, who is returning to the Kennedy Center to record for DEutsche Grammophon his new "Songfest." of which he gave the world premiere with the National Symphony last month.

For yesterday's sessions, the Columbia experts used 15 microphones, with two more out in the aisles at about row 10. A special platform was built directly behind Rostropovich's podium. On this, Stern could face the conductor and orchestra while playing, an arrangement which makes a better balance for recording than the usual position in which the soloist faces out into the auditorium.

In addition to the concerto, Stern and the orchestra also recorded Tchaikovsky's "Meditation", the music which the composer originally intended as the slow movement of the concerto.

It takes a lot of stamina, physical and mental, from everyone involved to play under such pressure for an entire day. It is a little living a whole day under a microscope.

But when it was over, Stern said, "Now we can play the whole concerto! I'm ready!" And Rostropovich, who says he never tries while working a quick runthrough ofthe Beethoven Triple Concerto.