"Multum in parvo," they said in old Rome, meaning "much in little." It is one of theater's major, ageless tricks and with economics more devouring than ever, much in little again in vital style.

This is why it is surprising explore, the Eisenhower's "Do You Turn Somersaults?" seems to ignore the obvious. In an apparent effort to relieve the potential monotony of two characters who only talk the production's nine scenes have been gussied up to fly, roll and revolve. Oliver Smith, as he always does, has created lovely etchings to feed our eyes.

But they quite get in the way of the deft, considered performances Mary Martin and Anthony Quayle are giving as this universal senior-citizen couple. Intensity of performance and accent on total simplicity virtually are blueprinted in Aleksei Arbuzov's script.

Should anyone watching these two players be concerned that it takes 20 unseen people to achieve the performance? No, but that's how many there are behind the sets, lights and sound. It costs money, too, some $67,000 to build the sets and $80,000 a week to meet the payroll. But aren't stylish productions getting out of style?

Play and performances would be better served by a smaller, more intimate theater such as the upstairs one the Kennedy Center hopes to have ready next summer.

Within two rooms of an Irish cottage, Brian Friel compressed much for "Philadelphia, Here I Come!," which ends its run Sunday at Olney. Friel allowed himself 14 characters which James D. Waring has east and directed with clean, winning simplicity. Several reviewers remarked that they'd forgotten what a fine play this is, but perhaps the truth is that so little mellow wisdom has been dramatized since 1966. Whatever, Olney has been showing us how much happened in these small rooms, while and Irish youth was preparing his assault on the new world.

Another case of much in little is the complex control of the National's "Man of La Mancha." While there have been scores of efforts to transfer Don Quixote to stage, musical or non-musical, film an puppetry, who would have thought that the character could be declineated at the same time an incident from the life of its author is framatized? But through the writing, music and Richard Kiley's dazzling performancein the dual title role, that is here achieved.

"Man of La Mancha" began in a theater seating only 200. Connecticut's Goodspeed Opera House. The initial production plan has been followed faithfully in the large theaters it since has played all over the globe.

Another example of much in little can be seen at the Barksdale Theater in Hanover, Va., some 90 miles south on Route 95.

This is an extraordinary little theater. In 1953 six young performers, most of them form Wayne State University's respected drama department, had wearied of New York's erratic, hit-or miss ways. A genial invitation from a Richmond lady to explore the area for potential audiences was speedily accepted.

In time half of the original six would be bought out by the others David and Nancy Kilgore and Muriel McAuley, who've nurtured almost every room back to life but still have some to go. Their pride is the basement theater itself, finally burrowed into the ground and boasting an accommodating thrust stage jutting into 200 comfortable theater seats.

Their first efforts were one-act plays and readings for neighbors. Then came the summer of '54 with three weeks of a full-length, "Gold in the Hills." Next came two-week runs, now expanded into as many as 12 weeks or more and a total of 152 productions.

"We never thought of ourselves as a dinner theater," says McAuley, "though we were the first in the state. We do serve dinner but not in our theater. It's country style in our five candlelit tavern rooms. Our theater is for theater only and we serve no liquor after our curtain time, 8:30. We're proud of sticking to that convenient, traditonal theater hour."

What goes on the stage, how well it's done, is the passion of McAuley and the Kilgores. They tap the best talents in the area and have uncovered some first-rate ones, including some other professionals who decided that New York wasn't the only place in the world where theater people could live.

Now, on Wednesday through Saturday nights, Barksdale is revealing, one of its occasional originals, a salute, "Red, Hot and Cole!" to composer Porter.

Here indeed is a finely honed, wholly professional creative musical any theater would be proud to present. It's clearly the work of dedicated theater people who decided that panic and hysterics could accomplish little. "We're never certain about the future," says Kilgore, "but we do know that we've survived through the best quality we can muster. Yes, we're small and we have no passion to over extend."

So, if "Do You Turn Somersaults?" were to narrow in on its small but potentially touching focus, it might still become a trim carriage for Martin and Quaylemultum in parvo.