THE SIDELINES : Soviet Leads in Pentathlon

Edward Zenovka of the Soviet Union took the lead in the World Modern Pentathlon Championships today with a third-place finish in the cross-country race.

Anatoly Starostin, another Soviet athlete, slipped to second after a 13th place finish in the cross-country.

Zenovka covered the 4,000-meter course in 12 minutes, 55.1 seconds and picked up 1,240 points. He leads Starostin 4,576 to 4,557 going into the final horseback riding portion Saturday.

Robert Stull, the American champion from Austin, Tex., dropped from fourth to 18th overall. Stull was 57th among 65 competitors in the cross-country.