Three Soviet runners took sick at exactly the right time for their country's Olympic team today. Their ailments enabled the USSR to field the best possible men's and women's 1600-meter relay teams -- and both won gold medals.

The Soviets substituted two women in the finals from the team that qualified Thursday. The men today brought in Viktor Markin, who won the open 400-meters Wednesday, for heat anchorman Viktor Burakov.

"All three (substitutions) were supported by medical certificates," said Fred Holder, senior member of the international Amateur Athletics Federation, According to IAAF rules, no member of a relay team may be replaced without such evidence. Two of the documents were for leg injuries, Holder said, the other for a sore throat.

Coincidentally, or perhaps not, the final two women runners on the Soviets' 1600-meter relay, Nina Zyuskova and Irina Nazarova, were their best 400-meter runners who also had a much-needed day of rest during the heat. The same held true for Markin.

Nazarova and Zyuskova finished fourth and fifth respectively in the women's 400 Monday. An 800-meter runner and a 400-meter runner who failed to make the finals were used to qualify the Soviet women's team. Nazarova barely held off Marita Koch of East Germany to win the relay gold today.

The Soviet men beat East Germany by two-tenths of a second.