Although part of "Major Barbara" takes place in a munitions factory, the only explosions you will hear at Arena Stage are those of a devilishly alert mind at work. Rebellious ideas hurtle up against entrenched beliefs, and out of the clashes emerge some tantalizing paradoxes. Since the mind in question is that of George Bernard Shaw, you may gather that it makes for quite an intellectual racket.

"Major Barbara" is one of the most discursive plays the grand man ever put to paper. Here he is virtually bursting with his views of morality, power, poverty, conscience and religion, not to overlook charity, the English and foundlings. And Arena Stage's largely satisfying production has discovered a very clever way around all that.

Yes, around it. Brilliant as Shaw's ideas often are, they tend to hog the spotlight with very little encouragement. What starts out as a play can end up looking suspiciously like a round-table discussion. At Arena, however, you will find yourself listening most attentively to the debates and the arguments, because on their outcome hinges a very elemental question: Will the boy get the girl?

Let me explain. At the outset, the play presents itself as a comedy of manners. The imperious Lady Britomart is fretting about the financial future of her three children, especially Barbara, or rather Major Barbara, ever since that vital young lady took it into her determined head to join the Salvation Army and save some souls. Barbara is being pursued by a charming professor of Greek, Adolphus Cusins, but there's not much money in Greek. And no money, no marriage.

Consequently, Lady Britomart has steeled herself for a confrontation with her husband, Andrew Undershaft, the titanically wealthy arms manufacturer she hasn't seen in 20 years. (She has always disapproved heartily of the ethics of his profession, but has come to recognize the utility of his millions.)

Already you see the trouble that is brewing. Being devout of purpose and dedicated to the poor, Barbara has no intention of taking a tainted shilling from her ruthless father. And Undershaft, being proud, combative and perfectly at ease with his conscience, has no intention of letting his daughter assume even a hint of moral superiority. He is also casting about for a successor to run his munitions empire, and in his crafty mind, Adolphus just might be persuaded to give up Greek for gun powder.

A battle royal ensues -- first on Barbara's turf, the squalid Salvation Army shelter, where she doles out bread and spiritual solace; and then in Undershaft's gleaming cannon factory, which is something of a workers' paradise, as long as everyone is careful to mind the matches. Each character tries to checkmate the other; the principles and counter-principles fly thick and fast; and comedy of manners has been left in the dust for Shaw's preferred form of dramaturgy -- the play of ideas.

Arena's production, directed by Martin Fried with an unbilled assist from Zelda Fichandler, has been very astute about these matters, however. The role of Major Barbara has been given to Christine Estabrook, an actress who has a most firmly feminine presence -- a rose with the stem of an oak, you might say. And the role of Adolphus has been conferred on Robert W. Westenberg, an enormously engaging actor who projects much of the modesty and gently self-disparaging aura of the early Jimmy Stewart. The two constitute a natural couple, temperamentally and physically, and your every instinct wants to see them mated.

That, though, will only happen if Undershaft's and Major Barbara's opposing philosophies can somehow be reconciled. Power and idealism, secularism and salvationism must be made to join hands, if ever the young lovers are to join theirs. Shaw will pull it off, of course, but in the meantime we are deeply committed to the course of the evening's arguments, and for far more than intellectual reasons. Biology is also exerting its claims.

To arrive at this kind of tug of war requires very deft maneuvering, and apart from some slack time spent in the Salvation Army headquarters, this production (Arena's third mounting of the work) is continually on its toes. As Undershaft, Biff McGuire is more than just a formidable opponent. Squinting at the children he's having trouble sorting out after 20 years, he's a bit of a social bumbler. But put him within spitting distance of one of his cannons, and he reveals himself as a flinty old rogue, full of flash and pepper.

Mikel Lambert plays his wife with authoritarian panache. As one of the souls Major Barbara wants to rescue from misery, Richard Bauer translates hypocrisy into a merry little jig. And Charles Janasz's portrayal of a boobish suitor is worthy of Max Wright, who used to get these parts in his halcyon days at Arena. (Where the evening does dip, mostly in its middle stretches, it's no fault of Arena's cast, but rather because Shaw takes one detour too many.)

Tony Straiges, surely one of our finest designers, has put selectivity to stunning use and come up with three handsome sets. Shafts of light stream though Victorian stained-glass windows, deepening the already plush red of the armchairs in Lady Britomart's salon. Wooden benches stripe the stage diagonally at the Salvation Army shelter. For the last act, he has constructed a mammoth cannon, which is boldly rolled out into the center of the stage. It is an obvious encumbrance to the actors, who must negotiate their way around it, climb up on it or peer under the barrel in order to communicate. But that is precisely the point. Philosophically, Shaw's characters are going through similar contortions in an attempt to accommodate themselves to the whole notion of massive firepower in the modern world.

Written in 1905, "Major Barbara" obstinately refuses to go out of date. The arms race, the debasing nature of poverty, the urge to save souls and the uselessness of saving them if they are not first well-fed, well-clothed souls -- all this has an especial pertinency to the Reagan years. But in a theater, the fate of the world can only command our attention for so long. What keeps us really tuned in at Arena -- all through the pros and cons, the ifs and what ifs of Shaw's passionate diatribes -- is the fate of a very appealing young couple. Basic as that!

MAJOR BARBARA, by George Bernard Shaw; directed by Martin Fried; costumes, Marjorie Slaiman; set, Tony Straiges; lighting, Hugh Lester; technical director, David Glenn; with Mikel Lambert, Kevin Donovan, Christine Estabrook, Robert W. Westenberg, Charles Janasz, Biff McGuire, Christopher McHale, Richard Bauer.

At Arena Stage through Nov. 22.