LONDON (AP) _ Martina Navratilova, the world's top-ranked player, will lead the United States team that will try and defend its Federation Cup championship in Canada this summer, the International Tennis Federation said Thursday.

Steffi Graf of West Germany, ranked No. 2 in the world and unbeaten this year, also will compete in the $325,000 tournament.

The annual team competition will have added significance, because the results will form the basis for the women's field in the 1988 Olympics.

The Olympic tennis tournament was opened to professional players this week by the International Olympic Committee.

The ITF said the U.S. team would be the same as the one that regained the Cup from Czechoslovakia last summer at Prague.

Navratilova will be joined by third-ranked Chris Evert, sixth-ranked Pam Shriver and seventh-ranked Zina Garrison for the July 26-Aug. 2 competition at Vancouver, British Columbia, the federation said.

Czechoslovakia is scheduled to send fourth-ranked Hana Mandlikova and fifth-ranked Helena Sukova, while West Germany will be represented by Graf, Bettina Bunge and Claudia Kohde-Kilsch.

Ninth-ranked Gabriela Sabatini and Mercedes Paz will comprise Argentina's team, while the Canadians will be represented by Carling Bassett and Helen Kelesi.

Teams have until two weeks before the draw to change their rosters. The draw will be held July 16 at Vancouver.