The sky was still bright at Wolf Trap as Ashley Lawrence signaled the orchestra for the first softly pulsing passages of Prokofiev's "Romeo and Juliet" score and the curtain rose on the Verona square where Romeo (Anthorny Dowell) pestered Rosaline. It was halfhearted ardor, he seemed relieved to join his two friends.

In the glow of artificial illumination and lingering daylight which unframed the stage and made the spectators part of this scene, the dancers were casual.Movement was subdued, gestures and expressions were understated. It was all so natural one had to remember that this is what Britain's Royal Ballet is all about - ease and measure.

The pacing quickened, of course, but never abruptly. Kenneth MacMillian's conception of a ballet we've seen here in at least three other versions within the year is almost all motion. There is less of facial expression and gesture acting than of movement characterization: Passages of full dancing emerge from the movement tableau.

It was in first dance, for Romeo and his two friends, that Dowell's performance began to smolder. Wayne Eagling as Benvolio moved with a free, open line in extended steps. Michael Coleman, the Mercutio, dances tautly these days. Dowell's ability to keep his line even in turns in incredible. He was always one of the most perfectly smooth of dancers in his former appearances with the Royal Ballet. This past year, with American Ballet Theatre, he was less perfect but learned brilliant phrasing.

Last night, returning to his alma mater on the opening night of its North American tour, Dowell combined that former perfection and the new brilliance His performance burst into flame when he encountered Merle Park, his Juliet. From that point on his acting and dancing were fabulous.

There were other notable renditions of roles with last night's fine British teamwork. Michael Somes' Lord Capulet conveyed sterness but also concern by his firm step and noble posture.

Leslie Edwards differentiated his two benevolent roles subtly.