Antal Dorati makes his debut as a television series personality tomorrow. And he turns out to be in an engaging one indeed -- as much as a commentator as a conductor.

In inteviews with actor E. G. Marshall, Dorati serves as host on public television's nine-part "Beedthoven Festival." Each segment Features a Beethoven symphony, with Dorati directing the Detroit Symphony Orchestra. The first hour airs tomorrow at 7 p.m. on Channel 26 and features the Second Symphony.

The lucidity, wit and authority with which Dorati discusses the Beethoven symphonies makes one regret that his gifts as a spokesman for music were not better utilized during his seven years as music director of the National Symphony Orchestra.

In tomorrow night's program Marshall visits Dorati in his Detroit study, where he is sitting at a piano with a fire blazing in the fireplace. The conversation focuses on the circumstances under which the symphony was written. Marshall observes that the Second is known as Beethoven's happiest symphony. And Dorati disagrees.

Dorati maintains that Beethoven symphonies are too complex to allow such simple categoriation.

"All these works are separate worlds into themselves, little microcosms with millions of moods. Anyway, how could anybody be completely happy under the desperation of just having realized that the hearing problem that had troubled him for five years was more serious than had been thought? He realized for the first time that it would be years before his hearing could improve and that the odds were that it would get much worse."

Then Dorati asks Marshall to read excerpts from the moving Heiligenstadt Testament, in which Beethoven declares that he has "had to cut myself off in solitude. How could I possibly refer to the weakening of a sense that ought to be more perfect in me than in other people... I came close to ending my own life, but my work held me together."

Then, with the piano, Dorati compares early Beethoven to late Haydn and Mozart; then describes his own view of the work, which follows in a tape of a Detroit Symphony concert.

All the performances were taped during the two-week-long Beethoven Congress in November 1977, during Dorati's first season as music director in Detroit. The Ford Motor Co. Fund paid for the series.

Subsequent programs confrm Dorati's skill in discussing music, all of it apparently extemporaneous. The second of the series features the Seventh Symphony and the third has the Sixth, or "Pastorale."

There is an element of provincialism in the production, as when Marshall begins the first segment by saying, while riding through a lovely neighborhood on the way to Dorati's, that Detroit "has been called an ugly cith." The message is that this is no longer true.

Later, interviews with Dorati are conducted at sites that show off the beauties of Detroit, however irrelevant they may be to Beethoven.

At one point tempestuous complexities of Beethoven from the deck of a Detroit River tugboat, with the new Detroit skyline passing in the background. Even there, Dorati is at ease and provocative.