How to choose records that let you hear the true Franz Lehar

It's about time Americans begin to take Franz Lehar a bit more seriously than they do.

This hit me during the first night of the New York City Opera's new production of ''The Merry Widow.'' New-old would be more to the point. Though the trappings are new, the feel, the low humor, the senseless reshuffling of the score all looked and sounded disturbingly like the production this new effort replaces. This is hardly the respectful ''Widow'' one had hoped for.

The eminent music critic Ernest Newman made a plea on behalf of Lehar in the early 1950s when Angel Records inaugurated an operetta series with a superb performance of ''Die Lustige Witwe,'' with Elisabeth Schwarzkopf, Erich Kunz, Nicolai Gedda, and Emmy Loose, conducted by the grand stylist Otto Ackermann. (The record has long been out of print domestically but is available in stores dealing in imports - EMI-Electrola 1C-49-03 116/17 - mono). In that essay Mr. Newman said: ''The man in the street may love 'The Merry Widow' but the musician , in addition to loving it, admires and wonders at it, so fresh and varied is the melodic invention in it, so deft, for all their economy, the harmonization and the scoring.''

Choosing records of ''Widow'' is not hard. The mono set just described is near-definitive. The remake, with Schwarzkopf, Gedda, Eberhard Wachter, Hanny Steffak, and Lovro von Matacic conducting, is exceptional too (Angel SBL-3630). Herbert von Karajan's conducting of the Berlin Philharmonic is stunning on DG 2707 070, but the singing is uneven. The newest Angel set (SZBX-3906) features Edda Moser as an average Hanna, Hermann Prey an enchanting Danilo, Helen Donath an adequate Valencienne. Tenor Siegfried Jerusalem sings Camille so lyrically (and often sweetly) that one questions how he manages the heavy Wagnerian roles he is now assuming. Heinz Wallberg is the able conductor.

Alan Titus is featured on Angel S-37500, which has highlights of the last previous City Opera production. Beverly Sills unfortunately is in erratic voice, and there's generally unacceptable singing from Glenys Fowles and Henry Price. Julius Rudel conducts. Joan Sutherland is featured on a disc of highlights from her husband Richard Bonynge's performing version of the score, which is not really any better than the Sills, particularly in the secondary casting (London OSA-1172).

Lehar is not known for ''Widow'' alone (except in the US), but for ''The Land of Smiles,'' ''The Count of Luxembourg,'' ''Giuditta,'' and ''The Tzarevitch.'' There is much good music in the these other works.

Lehar's ''Paganini'' is not as well known, but it has now been issued on disc in this country and is every bit the equal of some of the lesser operas that companies insist on reviving. It offers spendid vehicles for a stylish tenor and a lush-voiced lyric soprano. Angel SBLX-3863 boasts Nicolai Gedda in the title role and Anneliese Rothenberger as Princess Anna Elisa in an expert presentation under the direction of Willi Boskovsky, with Ulf Hoelscher executing the flashy violin cadenzas and solos.

Fans of operetta can get performances of the big Lehar works as well as all the famous operettas of Millocker, Kalman, Lortzing, Johann Strauss, and others in import stores. Arabesque Records is releasing some of them, and their efforts are to be encouraged (even though I have not actually heard the pressings). But the Schwann catalog does not list these works under the composer, only under title (in translation only, on the Musicals listing in the back).

Americans have been suspicious of operetta for years. When domestic companies think of operetta, it's usually ''Widow'' or ''Die Fledermaus,'' crudely done. The problems begin with the librettos - hardly the stuff of great theater or comedy, but retaining a certain validity when done with respect. Usually, directors feel they must rewrite the gags and throw in additional jokes to make it ''interesting'' for an (implicitly easily bored) American crowd. And then, most American conductors have little sense of how to imbue these scores with charm and lilt. At the City Opera, Scott Bergeson is young and seems more content to get through ''Widow'' rather than to show the audience just how beautiful and sumptuously orchestrated the score really is.

Bill Gile has directed at the Goodspeed Opera House, but I saw few traces of his influence on this, his debut production with the City Opera. The English version mentioned above is credited to Adrian Ross, and it is unsavory. The names are no longer the ones Lehar had. The humor is base, and James Billings and Jack Harrold - now offered automatically as the house comics - ham it up unstintingly.

Herbert Senn and Helen Pond will be remembered for many splendid sets at this house and for Sarah Caldwell in Boston, but not for this flimsy ''Widow'' with its less-than-attractive color schemes. Suzanne Mess's costumes glitter showily in the spotlights.

The casting on opening night was not from strength. The roster has sopranos with the requisite star-power for the role, but instead of bringing in, say, an Elisabeth Soderstrom - what an enriching experience that would have been for cast and company - Miss Sills used Elizabeth Hynes, who sings prettily but lacks presence. As Danilo, the suave Alan Titus seemed rather at a loss about what to do in this show. The all-important secondary story of the young lovers should have singers who convey youthful impetuosity. Susanne Marsee and Joseph Evans convey instead an indifferent flirtatiousness.

''The Merry Widow'' opened an acoustically revamped New York State Theater. It will return there during the fall season, and will be seen in Los Angeles in December. It is good to be able to report that the $5.3 million spent has done some good (see this column in the Monitor's Sept. 8 issue). Voices now have a presence in the hall, the dialogue was audible with a consistency and clarity unknown in the ''old'' days. The orchestra can be heard with new clarity as well.

Mr. Bergeson tended to swamp his singers, and I suspect most conductors will run into similar problems until they get used to the new sound.