THERE ARE those of us mainly interested in where we are, and others in where we are going. But it is always useful to know where we have been. This is as true in the arts as in other aspects of life--perhaps more so.

At any rate, the recent nostalgia boom in the musical theatre continues apace. The Spingold Theatre at Brandeis University has just kicked off its summer season by offering a sprightly production of Sweet Adeline, the 1929 musical by Jerome Kern and Oscar Hammerstein II, imported from a two-month run at the Goodspeed Opera House in East Haddam, Connecticut.

The Goodspeed operation is quite a story in itself. A campaign to save the old Opera House from scheduled demolition was successful, and the riverfront building was refurbished and reopened in 1963, functioning since then as "the only theatre in America entirely dedicated to the preservation of the heritage of the American musical and the development of new works." Among the latter are Man of La Mancha, Shenandoah, and the current Broadway hit Annie.

For each new work it spawns, however, the Goodspeed mounts two revivals, several of which have gone on to Broadway. In the case of Sweet Adeline, the work had until now never been revived since its original production.

Jerome Kern (1885-1945) was, with Irving Berlin, one of the two composers chiefly responsible for establishing the modern musical as an important theatrical genre. Kern was also the major stimulus for the young George Gershwin, and has remained an idol for the still-active Richard Rodgers, who celebrates his 75th birthday tomorrow.

Kern did his first solo musical in 1912, and during the First World War years pioneered the "intimate musical," designed for the 299-seat Princess Theatre, where big orchestras and casts, elaborate spectacle, and more than two sets were proscribed.

He continued to work on larger shows, however. Curiously, he first met librettist-lyricist Oscar Hammerstein II at the funeral of operetta-composer Victor Herbert in 1924, and they decided to work together. Their collaboration yielded Sunny the following year, and, most notably, Show Boat, which will have its 50th birthday next December.

There is universal agreement that Show Boat is Kern's supreme achievement and that the work as a whole is a peak in the history of the musical. Those who need to be shown why can catch a new production of it at the Barn Theatre in New London, New Hampshire, from July 19 to 31. In the 1927 original, the singing of "Can't Help Lovin' Dat Man" and "Bill" elevated Helen Morgan to stardom; and it was expressly for her that Kern and Hammerstein wrote Sweet Adeline two years later.

Adeline is no Show Boat, but it was initially well-received; and, despite the effect of the stock-market crash on the public mood a few weeks later, it managed a healthy 234-performance run. It has plenty of fine music and some good lyrics. The main trouble lies in its book, which is silly and amorphous (the same, in sooth, might be said about the plot of many a grand opera).

At least the tired formula of A loves-loses-regains B is avoided. Here, A loves and loses B but winds up happily with C (or, I should say, with D, since the current director Bill Gile has tinkered somewhat with the original script--to little avail).

The plot--such as it is--in which the signing-waitress in her father's Hoboken beer-garden, on losing her boyfriend, essays the New York stage and becomes a celebrity, is based to a considerable degree on the actual life of the show's star, Helen Morgan (1900-41), who told Kern and Hammerstein about her early years as a chanteuse in a German-style beer-garden named Adeline's. (A film biography of Morgan's life was made in 1957, starring Ann Blyth and Paul Newman.)

The show's creators were cashing in on the public's fascination with theatrical life, and with the disparity between onstage glamour and backstage heartache. The musical portrayal of stage life would, with the immediate advent of sound movies, be taken up in a host of Hollywood films such as The Singing Fool, Show of Shows, Hollywood Revue, Footlight Parade, Forty-Second Street, the Broadway Melody series, and the Gold Diggers series.

If Sweet Adeline in 1977 gives us a nostalgic look at 1929, the show itself attempted to give audiences of 1929 a look at a bygone era. The work was originally billed as "a musical romance of the Gay Nineties," and its story began in 1898. In the version at Brandeis, director Gile has omitted a military scene at San Juan Hill in Cuba, though the Spanish-American War is still invoked; and he has, at show's end, eliminated all reference to the celebrated murder of architect Stanford White by Harry K. Thaw only a few feet away. But enough remains to guarantee that we are immersing ourselves in nostalgia on two levels.

Kern went out of his way to establish period and atmosphere by opening the show with a potpourri of old-time numbers like "A Bicycle Built for Two," "The Band Played On," and "A Hot Time in the Old Town Tonight." There is also, for the piccolo-playing Dorothy, a punningly titled "Play Us a Polka, Dot," and, farther on, an example of the old unaccompanied barbershop quartet (actually a quintet here), "Pretty Jennie Lee." The opening scene, in proprietor Schmidt's beer-garden, provides the endearing folkish song "'Twas Not So Long Ago," which points to Schmidt's immigrant origins by being sung first in German by him and then in English by his daughter Addie; and this song easily survives its three reprises in later scenes.

At the Brandeis opening, director Gile had not elicited from his cast the remarkable ensemble precision that characterized his Goodspeed revival of Kern's Very Good, Eddie two seasons ago (which I saw in its Broadway transfer) and of Hirsch's Going Up last summer (which I caught on its home stage). But one must take into account the fact that the cast was in strange surroundings, and, further, that three of the important roles were assumed here by players who had not done them in Connecticut. In this respect, Gile's guilt will doubtless become Gile's gilt as the run proceeds. Clearly he does know the style of the period, and his direction is almost always inventive, often hilarious, and sometimes touching. There were a few times when the staging was too cramped, but one must remember that the sets and blocking were designed for the Goodspeed's restricted space. Incidentally, Edward Haynes's sets are just charming--as is Dan Siretta's choreography.