Chester A. Crocker, U.S. assistant secretary of state for Africa, left here tonight saying he had a better appreciation of the gap between the country's race groups but still did not believe in economic sanctions as a way to end its apartheid system of segregation.

A return to economic growth and stability, Crocker said at an airport press conference, was the only way for South Africa to get back on the road to building a just and equitable political system.

"We don't seek to wage economic war on South Africa and its people. We don't think that is going to help. We don't think reform can flourish in a climate of economic decline and deterioration, so our view on that hasn't changed," Crocker said.

The assistant secretary was noncommittal when asked to predict what President Pieter W. Botha, with whom he talked for 90 minutes yesterday, might say in his crucial state-of-the-nation speech to Parliament Jan. 31.

Six U.S. congressmen, led by Budget Committee Chairman William H. Gray III (D-Pa.), told reporters after meeting with Botha Thursday that they believed he would have no substantial reforms to announce.

Three days later Fritz Leutwiler, a Swiss banker appointed to help negotiate a rescheduling of South Africa's foreign loans, said after meeting Botha he was optimistic about the prospects of a major reformist statement. South Africa's loans were frozen when international banks demanded repayment following pressure from opponents of apartheid.

"I don't wish to contribute to speculation about what President Botha may say or give the impression that I know," Crocker said.

"I think we leave with a somewhat better information base as to what some of the possibilities are and what some of the obstacles are but I am not going to declare myself anything more than a realist," he added.

Crocker said he had delivered a letter from President Reagan to Botha, and this had provided the basis of his discussion with the South African government.

The assistant secretary did not disclose the contents of the letter, except to say it covered internal developments as well as regional issues in what he described as the "frankly dangerous" southern African region.

In an oblique criticism of widespread condemnation of South Africa by Americans, Crocker said it was now time "for the world to pay attention to what South Africans think, what South Africans are prepared to do, what risks they are prepared to take for peaceful progress."

"Here in South Africa is where the action is," Crocker added.

South Africa's different racial groups needed to find each other, and the United States wished them well as they tried to do this, he said. "We want South Africans to succeed. That is the side we are on," Crocker said.

Crocker's visit was welcomed by the progovernment Afrikaans language press as indicating warmer relations between Washington and Pretoria.

Crocker, who has been criticized for meeting few blacks during his visits here, this time visited one of the strife-torn black townships, Duduza, where one of the community leaders he was due to meet was killed before he arrived.

"Obviously there is more interest and there is more going on in the townships than was the case in the past, so perhaps it is not surprising that their situation received more attention," Crocker added.