At both 33 (her age) and 33 1/3 (the speed of her albums), Olivia Newton-John has gone through drastic changes. She has not abandoned but she certainly has outgrown the eternal inge'nue image that threatened to make her a Sandra Dee for the '80s, a limiting sentence she deserved to be free of after the '70s. Newton-John toughened up her voice, her repertoire, her whole musical approach; she got "physical" as well as social and subtly political, trading cuteness for acuteness.

At the Merriweather Post Paviliion last night, she displayed all her endearing charm in a 90-minute show that began with a montage of photos and news clips that Newton-John proceeded to enliven and to live up to. The material ranged from her mildly controversial country-era selections to quick stops for "Grease" and "Xanadu" and a slew of hits, old and new.

The slinky rock of "Make a Move on Me" aside, Newton-John is an engagingly direct performer, less vampirish than coltish in her stage demeanor and kittenish in her delivery of ballads (especially the lovely "Falling" and the subtly seductive "A Little More Love"). Just as she has begun taking risks in her career, Newton-John is stretching her sweet, albeit thin, voice via aggressive and uptempo songs like the new tough-edged "Heart Attack," Dolly Parton's skittishly challenging "Jolene" and her own "Physical" anthem.

With the tight backing of a Tom Scott-led septet and three backup singers, Olivia Newton-John proved herself an able entertainer commercially shrewd enough to move out of the middle of the road into the fast lane. A little "Grease" seemed to have helped a lot.

She returns to Merriweather Post tonight.