President Carter has decided to split his trip to nine countries into two segments, with the first segment tentatively planned to begin during the week after Christmas, it was disclosed yesterday.

Zbigniew Brzezinski, the White House national security adviser, told reporter yesterday of the plan to split the journey into two separate trips and that the first trip would begin during the week between Christmas and New year's Day. The second trip would take place in the spring, he said.

Brzezinski provided no additional details. However, other sources said that of the nine countries Cater initially planned to visit, the two stops in South America - in Venezuela and Brazil - were the most likely to be postponed until the spring.

The other countries that the President was to visit were Nigeria, Saudi Arabia, India, Iran, France, Poland and Belgium.

Carter orginally was to leave Washington on Nov. 22, visiting four continents and covering 25,000 miles hald-way across the world and back in 12 days. He postponed the trip three weeks before he was to leave, saying he wanted to remain in Washington until Congress completes action on his national energy plan.

Sources stressed yesterday that most final decisions on the President's new itinerary have not been made. They said the trip being planned for late December would last more than a week, getting Carter back to Washington before Congress convenes for its new session.

Several travel options were still under study at the White House, the sources said. One of them, for example, would have the trip begin in Europe, a reversal of the original plan in which the President was to begin his journey in South America, go on to Africa and Asia and wind up in Europe.