WASHINGTON theater-goers are understandably upset about the high cost of tickets. And they are high -- too high for most people.

Yet, with the highest per-capita income in America, Washington has lower ticket prices than cities with less money to spend. A few examples:

The rivival of "Oklahoma!" played the Kennedy Center Opera House at a $17.50 top. It went on to a $20 top in Philadelphia -- which ranks 16th in per-capita income in a listing of 22 "road" cities. When the show opens Dec. 13 at New York's Palace Theatre, it will have a $24 top on Friday and Saturday nights.

When "A Chorus Line" last played here, its top was $17.50, but the figure was $18 in Baltimore. In per-capita income, Baltimore ranks 21st in the list of 22 cities, just ahead of San Diego. The top was $18.50 in Philadelphia and continues in New York at $25.

On its late-summer visit to the National, the returning "Timbuktu!" was getting $18.50 on Friday and Saturday nights with second balcony seats at $12.50, $11.50 and $10.50. (In 1948, when the National went dark for four years, the top balcony was 55 cents, orchestra $4.40.) In Boston, ranked just above Philadelphia on the per-capita income scale, "Timbuktu!" had the same top as it did in New York, $19.50.

Deathtrap," still running in New York, has a top price of $17.50, but when it played the Eisenhower, the top was $15, against the $16.50 the same company got during its Los Angeles run.

A drama with only two players, "The Gin Game," rose to a $20 top during its long New York run. When Hume Cronyn and Jessica Tandy played it in Chicago, the top was $16.50, but when they came to the Kennedy Center, the top price was $15.

Because "Peter Pan" and "Snow White and the Seven Dwarfs" are considered prime fare for children, Washington consumers have been aghast that their prices are not scaled down accordingly.

When "Peter Pan" was at the Kennedy Center, it cost $17.50 for orchestra and front mezzanine seats and $20 for the boxes -- not usually found in most theaters. In New York its present top is $22.50.

"Snow White," created for Radio City Music Hall's 6,000 seats, was scaled there for a $15 top, with $8 the fee for the upper balconies. When the company of 85 opens on Dec. 12 at the National -- which seats 1,680 -- it will be scaled from $9 to $18. That's the only instance available records show for a touring production to charge more in Washington than it has in New York.

Conductor Lehman Engel, who has become the country's most knowing recorder of American musical plays, sums up the main reason for rising ticket prices succinctly with a few words about "Oklahoma!":

"In 1943 the original production cost $80,000 to mount. This new production is financed at $1 million. The top price for the orginial production was $4.40. The top for the present revival will be $25, or just under six time what it was in 1943. But the revival is costing over 12 times as much to produce." Tickets prices, Engel concludes, have not kept up with production costs. The Audiences

One recent table claims that of the nation's three top leisure activities, films attract 45 million persons a year, who spend about $200 million. Broadway is said to attract 9.8 million people and about $137 million. Sports is ranked third, drawing 6.7 million people who spend about $50 million.

For those who go to the theater, New York's ticket prices are the highest in the nation. The expense-account crowd, wanting to "see hits" rather than "go to the theater," can cough up $50 a pair for weekend nights. There's also the matter of parking fees. The Kennedy's $2.50 is cheaper here than the $3 to $4 charged under cover -- if you can get in -- downtown, or the Manhattan common-place of $5 to $6 for three to four hours.

In his study of the 22 road cities, research director George A. Wachtel of the League of New York Theaters and Producers notes that "the fortunes of economic growth have graced some U.S. cities far more favorably than others. Nominal personal income levels are often used as a measure of a city's wealth. But cost-of-living differentials are so great among road cities as to produce a complete reordering when they are introduced."

In terms of per-capita personal income, Wachtel ranks the top six as Washington, San Francisco, Chicago, Seattle, Houston and New York. Boston and Philadelphia rank 15th and 16th, with Baltimore and San Diego at the bottom.

The League has been investigating its audiences, and has found that in New York 52 percent of theatergoers are under 35, that 78 percent of them are white, and 77 percent earn more than $15,000 annually, that 68 percent have "some education" and that 53 percent are female.

Last June, the League looked into its Washington audiences, where the same statistics prevailed with two noteworthy refinements. Here 45 percent of theater audiences are college graduates -- a specific evaded in the New York categorizing -- and 46 percent of them earn more than $25,000 a year.

One must allow that statistics may be less illuminating than self-sustaining, but some facts do emerge from these figures. Washington audiences are better educated than average, and while their salaries -- or expense accounts, if any -- don't match those of mighty New York executives, the average here is higher and more secure. The Theaters

As this observer has been noting, there are Two American Theaters: New York's and the Rest of the Country's.

New York's commerical theater is loosely grouped into The League of New York Theaters and Producers, operating Broadway and "road" theaters.

The Rest of the Country's professional theaters are comparable to Arena Stage and the Folger Theatre Group. There are 157 of these in the League counterpart -- the Theatre Communications Group (Tgg) -- some of them working under contracts of the League of Regional Theaters (LORT).

Ticket prices of LORT and TCG are considerably lower than the League's scales. And again, Washington TCG-LORT ticket scales are lower than elsewhere. Arena Stage this year has gone to a $10.50 top, and the Folger's most expensive seats are $10 for Friday and Saturday nights.

Compare these with $12.50 for San Francisco's ACT (American Conservatory Theater), the Los Angeles Mark Taper Forum at $13.25, Chicago's Goodman at $11.50, Minneapolis' Guthrie at $10.45, all on a comparable level. The Brooklyn Academy of Music has the top price of $14.50, and the Anchorage, Alaska, Repertory Theater goes to $10.50 in the country's most expensive city. The only cheaper houses on the TCG-LORT major list are Baltimore's Center Stage at $10, Richmond's Virginia Museum Theater and the Seattle Rep at $8.50.

In practice, TCG-LORT theaters have lower scales than these single ticket maximums reflect. All offer subscription plans that are not available to the New York League's setup since commerical productions are mounted as single, oneshot gambles.

This means that Arena Stage's advance discount plan gives buyers a 20 percent saving on eight plays, as much as $14.20 in some seating areas, $10.20 in others.

The Folger's subscription scale, including seven productions -- five in its 210-seat home, two of them in the Kennedy Center's 500-seat Terrace Theater -- ranges from $36 for persons "under 21/over 65" to $70 for Saturday night seats.

Arena's and like theaters' prices have risen relatively modestly. In the 1977-78 season, Arena was selling its lowest priced seats at $4.25; they now go for $6. Its top then was $8.50, it is $10.50 today. But to mention only what homeowners dont't need to be told, air-conditioning and heating bills have trebled. Broadway Costs

Why do Broadway and touring attractions cost so much more than the TCG-LORT productions? This is an area about which books and 1,000-page reports have been written, so a few details must be used to suggest many:

Commerical theater exists for profits. Nonprofit theaters are almost all "debt-funded."

Theater buildings themselves are valuable real estate, taxed and mortgaged accordingly. But they are income-producing only three hours out of 24.

Those producing commerical plays no longer use their own funds. Through "angels," they accumulate capital to finance productions, keeping 50 percent of the profits, it any, as their share for pulling the maze together. "Angels" will be lucky to get any percentage whatever of the 50 percent that might accrue in the profit column. As Herb and Dorothy Fields had that old Indian chief say in "Annie Get Your Gun" -- "Never put money in show business."

It takes dealings with about a dozen unions to produce a straight play, with as many as 18 to mount a musical. When producers don't own theaters -- and only a few do -- they make intricate deals with theater owners. Wise is the producer who employs smart lawyers.

Owing to contract stipluations worked out during the '70s, when a production goes on the road -- either for tryouts or for post-New York tours -- all hands now receive per diem for room and board in addition to their salaries.

Because of the increased use of TV spots, among other factors, advertising costs have risen fivefold in the past six years. Advertising is vital to survival.

Tryout costs can zoom. When a song in a musical is cut and a new one substituted, it means new orchestrations for 26 musicians, all hand done by skilled copyists. It can mean throwing out costumes and scenery and replacing same with new designs and materials.

There's such a thing as a "stop clause," by which theater owners can swiftly boot out attractions that don't hit instantly. This deprives modestly received ventures the chance to "find" potential audiences.

Price scales and cost rises are being watched more closely than ever by the League and TCG, both of which have alert research departments to which members supply figures with the impetus that all will benefit from this new, relatively rare, cooperation.

Currently represented by "Sweeney Todd," Washington-born New York producer Richard Barr heads the Broadway League; when referring to statistics, he draws a bleak conclusion:

"Obviously, we're not charging as much as we should, and I see things going higher. This New Year's Eve, for instance, look for a $35 top at the big musicals.

"Of course we don't like it, but the fact is that over the last 50 years the top ticket price of a musical has decreased 13 percent in real money terms. Because dramas have less chance for big success, the top price for straight palys has increased 25 percent. But those increases are far, far less than increases for food and fuel, shelter and clothing and pure luxuries."

The League's recent, highly visible TV commericals, soon to extend to European cities, have been attracting larger audiences and grosses than ever before to New York's stages, magnets to the City's vital tourist trade. Uncertain Future

The high cost of drama and the attractive demographics of Washington's audience are facts that certainly have not escaped the researchers who are likely to recommend ticket-price increases.

His peers are muttering enviously about Roger L. Stevens' early awareness of the capital's potential audiences. Because he can afford to be its unpaid chairman, refusing the usual managerial profits, Stevens literally helps keep down some Kennedy Center expenses.

So do Thomas and Zelda Fichandler at Arena Stage, who are paid much less than what their counterparts receive in regional theater.

"Our organization," says Thomas Fichandler, "is rooted in keeping prices low. Artistically I'd stack us up against any theaters, nonprofit or commerical.But with the foundations pulling in because they don't have the funds they once did, we are deep into deficit funding.About three-quarters of the way through each performance, I think to myself, 'Here's where we start getting into debt.'"

So, while theater tickets are still cheaper here than elsewhere, it may not continue indefinitely.