SINCE styles change in clothes, headdress and automobiles, is it surprising that dramatic fashions do too?

The National's "Anna Christie" by Eugene O'Neill is unmistakably a play of its period, the early '20s. As certainly, the Kreeger's "Catsplay," by Hungary's Istvan Orkeny, is of today's genre.

"Anna Christie" is in four acts that take place over a two-Week period. Alexander H. Cohen's production drops one of the original three intermission, accenting the play's virtue of allowing the players and audience the luxury of long, sustained scenes. This quality of continous action and emotion distinguishes the old form from the new.

"Catsplay," which details the relationship of two sisters through 65 years, dips in and out of time, a scene here of the present, a memory there of the past, an awareness that one impression is no more reliable than another. It is infinitely trickier in style than O'Neill's and in broad terms can be said to be a total reversal in style.

Both plays have in common superb roles for women and in both you find actresses worthy of their material: the celebrated Liv Ullmann as Anna and the relatively unknown but splendidly experienced Helen Burns as Orkeny's Mrs. Orban.

As though recognizing the unfashionableness of the structure of "Anna Christie" as well as the particular star quality of Ullmann, director Jose Quintero treats her as the gem she is. THere are times when Ullmann is seated and bathed in light at stage center while decisive action goes on behind her in the murkiness of stage left.

The actress, fully capable of this superstar treatment, is at all times engrossing. With that ability to wear what might be called peasant garb (also in her movie roles in "The Emigrants" and its sequel, "The New Land"), she walks and sits uncommon ease in the clothes and shoes Joan Greenwood cannily has chosen. She listens with uncommon intensity. Perceptions pass through her eyes and the import of the action behind her is clearly transmitted to us as it seems to her, which is a laudable detail.

Not the least of Ullmann's portrayal of Anna is her vocal strength. It is intrinsic to the character that, raised in a hearty Minnesota, this daughter of a Scandinavian seaman have a robust voice. Just as important, vocal projection is, or more accurately should be, part of and player's equipment.

This business of knowing use of vocal potentials also has gone out of style, reflected in the relatively light voice John Lithgow brings to the character of the surly stoker Mat Burke who decides, against his instinctive and religious senses, to marry a self-revelaed prostitute. Lithgow's record shows him to be a good actor. But vocally he is one of the mass of young Americans who seem to know nothing about projection, pitch and resonance. The result is that his major speeches - and O'Neill wrote some long ones - smack of a whining quality at odds with Mat Burke, making the stoker younger, more of a lightweight than he should be. Ullmann's vocal power makes Anna twice the person Mat is.

To O'Neill scholars, "Anna" is a gripping illustration of how O'Neill wrote. Originally the play centered on Anna's father, Chris Christopherson, and even was named "Chris" after the character and even later "That Ole Davil" from his pervasive line. The 1919 original version of Anna was of a pallid, inconclusive young woman, and not even the young Lynn Fontanne, who created her, could make much of Anna in Atlantic City and Philadelphia, after which the play was revised.

Anna, as well as Chris, was vastly sharpened in the two years before the material became "Anna Christie", and the part would reward such diverse types as Pauline Lord, Blanche Sweet, Greta Garbo and Gwen Verdon.

Critics then and now complained of "the happy ending," implying a commercial comput by O'Neill. He denied the copout but agreed that the uncertainty he wanted about the couple's future did not come through sharply enough. By using the father's "dat ole davil sea, she know" as the final line, he had intended fatalistic uncertainty. Maybe, he said, he should have titled the play "Comma."

As Mrs. Orban, the Kreeger Theater's Helen Burns has as showy and demanding a part. Mrs. Orban has two dominant qualities: self-delusion and joy. Alienating her daughter, worrying her sister, outraging the fatuous old tenor for whom she's had a lifelong passion, Mrs. Orban arrives at suicide, though her life force revolts. She winds up, to Orkeny's refined purpose, frivolously meeowing with her dippy friend Mousie, so blithely acted by Paula Trueman, making even sister Giza unbend. Katherine Squire plays Giza to restrained perfection.

Director Edward Payson Call's excellent cast also is distinguished by Eunice Anderson's sharp, waspish portrayal of Paula, a keen, knife-sharp characterization.

Above all, the tempestuous, scatter-brained, purposeful Mrs. Orban is a glorious creation, funny and immensely touching. Helen Burns plays her with bravura finish, a portrait the equal of Ullmann's Anna. To see both in quick succession is to rejoice that two such exceptionally fine actresses have such worthy roles.