OF THE area's major professional theaters, only one is run on a purely commercial level, the WarO ner. All the rest are nonprofit.

And at what house has that riskiest of commercial ventures, Shakespeare -- in the finest production seen here in years -- been playing? The Warner, with James Earl Jones and Christopher Plummer teamed in "Othello."

Surely this has to strike the inquiring playgoer as curious.

Theatrical maneuverings are getting curiouser and curiouser here and across the country, shifting phenomena worth noting. Sometimes it's getting so that you can't tell the nonprofit theaters from the strictly commercial ones. A brief survey, locally and across the country:

The National has had a new surge of life under Maurice Tobin. The 146-year-old stand is astutely booked through New York's Shubert Organization, although trouble may be brewing in that arrangement. Its nonprofit status is carefully protected by free daytime attractions, special children's programs and public services not found at commercial ventures.

Yet it has opened its season with a decidedly commercial smash, "Evita," born for profit in London and now a long-run resident in three American cities. Its next major attraction of the '81-'82 season will be Joseph Papp's pop revival of "The Pirates of Penzance," introduced under the nonprofit aegis of his New York Shakespeare Festival. As with "A Chorus Line," similarly created, its box-office returns are poured back into Papp's unique, immensely creative organization.

Arena Stage, a trail-blazer of the nation's nonprofit professional theaters, has just had its first unbroken summer, thanks to the hit Stephen Wade has had with his "Banjo Dancing" in the smallest of its three halls. With Pat Carroll's glorious Gertrude Stein portrait and the return of the Flying Karamazov Brothers to the Kreeger, the largest space will resume with Shaw's "Major Barbara" next month.

Shaw's Salvation Army story is one of that socialist's most pungent comments on money and the making of same. With women's rights and munitions as its topics, this, for all its years, can be guaranteed as timely and a likely box-office success.

Like all nonprofit theaters, Arena has to have commercial, public success. One experiment out of eight productions can turn the season ink from the normal pink to blood red. On occasion Arena has dramatized this by halting a performance three-quarters through, resuming after it's been explained that here is where the grants and income ran out.

One might have expected the Warner's sterling "Othello" to have played the nonprofit Kennedy Center. It was created at Connecticut's nonprofit American Shakespeare Festival, for which the center's eclectic Roger L. Stevens has been both an active and generous patron in the past. But last season's miserable "Richard III," with Michael Moriarty, evidently alarmed Stevens enough that he chose to avoid a second Shakespeare production.

Because there are no federal funds for Kennedy Center productions, nor have there ever been, its offerings are generally chosen for availability, viability and the hope that its private-productions money may be ultimately rewarded, as has been the case with "Pippin" and "Annie."

What is remarkable about the nonprofit Folger Theater Group is that with only 210 seats it has achieved the respect it has. Louis Scheeder, associated with the group since its 1971 start and its producer-director for the past eight seasons, makes his farewell with the current "Julius Caesar." Scheeder announced that he needed $1.3 million to produce the four Shakespeare plays scheduled; the Folger could assure him only a million. An artistic shift of some kind will be needed under actor-director John Neville-Andrews, Scheeder's successor. But the Folger's basic policy is clear and logical: performances of the works for which the Folger Shakespeare Library exists. The limitations are patent, but the imagination can still soar.

The least creative of our nonprofit theaters -- and possibly the most financially resourceful -- is Ford's. Its programming vacillates between what happens to be cheap and available from elsewhere -- last spring's "I'm Getting My Act Together and Taking It on the Road" -- or some gospel variation, begun with "Godspell" and "Your Arms Too Short to Box with God" to the current Christmas salute, "Black Nativity," yet another rendering of Langston Hughes' long-loved work.

Elsewhere, the liaisons between nonprofit and commerce are endlessly developing, and not always in the expected ways.

Noting all the arts centers elsewhere, Chicago recently realized it has none; efforts are under way to create one. But will Mayor Jane Byrne allot the $18 million needed?

Columbus, Ohio, is severing its Veterans' Memorial Auditorium connections with the commercial Kenley Productions, long its tenant at a modest rental. When the city booked Liberace this summer, he made a larger profit in one night than Kenley had in a week's run.

Worcester, Mass., creating a civic center for what it thought would be $8 million, ran into a cost overrun of 66 percent, and the state will chip in more than $10 million. (The state's art lottery folded this summer without ever having paid a dime to the arts.)

In San Francisco, lively, young and frankly commercial Carole Shorenstein, with the Nederlanders as her New York-based associates, has turned the Golden Gate and the Orpheum to live theater and is running the old Curran as well. Next door to it, at the Geary, the nonprofit American Conservatory Theater is running into tough economic facts.

These instances, like those in scores of other cities, are rooted in constantly rising costs. Big musicals now are budgeted at $2 million and straight plays are costing close to $1 million. Commercial theaters frequently consider nonprofit originals in hopes of cutting down costs.

New York's Lincoln Center was created by federal, state, county, city and private funds, but just ahead lies an even more intriguing Manhattan development.

This is the hoped-for restoration of nine stage theaters along both sides of 42nd Street between Broadway and Eighth Avenue, a project of the League of New York Theaters to abolish the area's -- indeed the city's -- seediest street.

Involved in this, on the public level, are the State Urban Development Corp., the New York City Department of City Planning, the New York City Public Development Corp. and the New York City Board of Estimates. Leading the private money interests, which so far have submittted nearly 30 separate plans, are the Shuberts and the Nederlander and Brandt organizations.

Of all the current alliance curiosities, none can top Dickens' "The Life and Adventures of Nicholas Nickleby," opening on Broadway Saturday night. This two-part production was created by Britain's subsidized Royal Shakespeare Company, using 60 actors for more than 100 roles. Incredibly, the Nederlanders and the Shuberts, ignoring their rivalry, have joined forces for this with Broadway's golden girls, Elizabeth McCann and Nelle Nugent. To pay the freight on the run, limited to 14 weeks in the 1,084-seat Plymouth (a Shubert house), tickets were priced at $100 for the two-performance, eight-hour production. A prime example of nonprofit and commercial linkage.

Both here and across the country, the distinctions between commercial and nonprofit bookings may sometimes blur, due to a variety of reasons. Considering the Warner's beginnings as a vaudeville-cum-movies palace, one can't help wishing the venturesome Sam L'Hommedieu well. He is playing the only strictly commercial theater game in town (Gateway's and the other dinner theaters are in a more modest league). Whether "Othello" will have paid its way after today's finale is yet to be toted up. What has mattered is that, led by the fine speech of Jones and Plummer, the play has been intelligible in the large house. No mikes!

Shakespeare was, after all, the most commercial of playwright-actor-managers. For all the nonprofit competition, life hasn't changed all that much in "Othello's" 377 years.