This quartet just keeps going and going and ...

When the Guarneri Quartet was just getting started some 35 years ago, one colleague, noting the members' strong and distinctive personalities, predicted: "It will never last."

Time has disproved that prediction.

Over the past 3-1/2 decades, the quartet has distinguished itself not only as one of the most accomplished ensembles in the world, but also as the longest collaboration of any quartet in existence.

The members - violinists Arnold Steinhardt and John Dalley, violist Michael Tree, and cellist David Soyer have performed more than 3,000 concerts around the world, including a performance at the White House. They have produced more than 50 recordings and received 14 Grammy nominations.

The group's longevity is a remarkable feat, especially considering their history of extensive touring. Sometimes they perform up to 125 concerts a season, spending more time with each other than with their families. A creative attitude has sustained this long marriage.

They socialize very little with each other outside the professional arena. Most often they make their own travel arrangements to suit individual preferences. Mr. Dalley, for instance, drives to performances whenever possible.

They resolutely avoid any post-concert analysis, but never flinch from arguments during rehearsals, which to this day are often charged with the heat of strong convictions. "We argue a great deal, but we don't quarrel," Mr. Soyer explains. "We start out with the idea that we respect our colleagues, so we don't take criticism personally.... Everyone has a very good sense of humor, otherwise we never could have existed this long."

The quartet is thoroughly democratic, which is not unusual these days but was rare when the group formed in 1964. "Audiences in Europe were shocked to think we had no leader, no dominant figure to decide repertoire and policies," Mr. Tree recalls.

The members of Guarneri proposes and informally vote on their repertoire, an expansive 100-plus works. The group never performs a work, even a standard piece, to which any member objects.

Though the bulk of their repertoire is mainstream chamber music, they often bring to light little-performed works of the 19th century and occasionally commission new works. The National Symphony, based in Washington, D.C., has commissioned for them a concerto by Richard Danielpour for next January.

With the grind of touring, one might suspect a certain staleness to creep into pieces they have performed, some more than 100 times. "We mine these pieces and find new things in them all the time," Soyer says. "Besides, we're all changing as people, and our ideas about the works change and that keeps it fresh."

Freshness also comes via individual musical experiences: During the three months the quartet spends apart, each player is involved in solo efforts and chamber music with other players.

When they are not performing, the quartet members teach at the Curtis Institute in Philadelphia, and are in residence at the University of Maryland in College Park. It was at Curtis that three of them met as students in the 1950s. They discovered Soyer at the famed Marlboro Music Festival in Vermont, where all were participating.

As Steinhardt notes in his engaging and eloquent new book, "Indivisible by Four" (Farrar, Straus & Giroux), all four had recognized talents as soloists, but chose instead the "communal pleasures" of chamber music.

Shortly after forming Guarneri, they took over much of the performance schedule of the retiring Budapest Quartet. Success came quickly and decisively. They called themselves Guarneri after the 17th- and 18th-century Italian family of string-instrumentmakers.

Today, the foursome has slowed its pace of performances. to 50 or so per year. They released two new CDs this season - Mendelssohn's Quartet No. 3 and Octet (Arabesque) and chamber music by Janacek (Philips Classics).

While some of the group's technical flash has dimmed, the sound is still distinctive: four equal voices, fluid and supple, capable of lush blend or striking individuality, who trade melodic lines with the delicacy of a whispered good night or the muscular vigor of heated discourse.

The group has given little thought to the future. By all indications, it will simply go on and on - and that's the way they like it. Says Steinhardt, "There is simply nothing better than playing string quartets and performing them in public."