Sen. Nancy Landon Kassebaum (R-Kan.), chairman of the Senate's Africa subcommittee, yesterday called for replacing the U.S. ambassador to South Africa to signal America's growing discontent with that white-ruled nation's policy of racial segregation.

While the current ambassador, Herman W. Nickel, has done "a very good job," she said, it is time to have "a new ambassador more visible and active in promoting our policy there."

Kassebaum's call for Nickel's resignation is particularly significant because she has opposed legislation calling for imposition of economic sanctions on South Africa.

It appears to reflect the general shift in Congress, even among conservative Republicans, toward a more assertive U.S. policy to pressure South Africa into making changes.

Kassebaum made her views known in an interview published in the Kansas City Times and confirmed them yesterday in an interview.

She said she felt the time is opportune "to look for some one else to show we are going to move our policy along rather than having the administration's policy forced" by Congress, where a number of economic-sanction bills are under active consideration.

Kassebaum said she has conveyed her views "for several months" to the assistant secretary of state for African affairs, Chester A. Crocker.

She said Crocker opposed the change of ambassadors as sending "a wrong signal."

"I personally feel we could send a strong signal, not a wrong one," Kassebaum said. "There needs to be a different sort of pressure at this time."