Jiri Sejba went from little-known to national hero by scoring a hat trick yesterday to lead Czechoslovakia, the host team in Prague, to a 5-3 victory over Team Canada for its first World Ice Hockey Championship title since 1977.

Sejba, a left wing, cut a 2-2 tie at 13:00 of the second period with a power play goal accomplished despite the presence of three Washington Capitals on Team Canada. Forechecking high on the point, Sejba stole the puck from defenseman Larry Murphy, was chased down the rink by Scott Stevens, pivoted around him to break free, skated in on goaltender Pat Riggin and deked him as well.

Team Canada had twice tied the score, Steve Yzerman and Rick Vaive matching goals by Sejba, but now the Czechs went up, 4-2, on Darius Rusnak's power play goal in the final period. Stevens cut the deficit to 4-3, stuffing the puck under goaltender Jiri Kralik.

With 96 seconds left, Coach Doug Carpenter pulled Riggin, and when a Canadian made a sloppy pass, Jiri Lala picked up the puck, scored into the empty net and assured that Canada would have to settle for silver.

The Soviet Union, 1978-84 world champion, trounced the United States, 10-3, for the bronze. The U.S. lost four straight after a strong preliminary round in which it beat Czechoslovakia and Canada.