A sudden slowing yesterday of the exodus from Cuba spurred U.S. officials' hopes that the month-long boatlift is beginning to wind down.

Only 25 boats, carrying 919 passengers, had arrived by 9 p.m. as the 32-day total topped 67,000.The slowdown may have been related to heavy thunderstorms at the Cuban port of Mariel.

Tuesday's total of 114 returning boats and 4,642 refugees had encouraged U.S. officials, who believe only about 500 boats remain at Mariel. Havana Radio put the total at 697 late Tuesday.

Some Cuban-American leaders were in Washington yesterday trying to persuade officials to let more boats go the Cuba. They say they're concerned about Cubans who will be left in Cuba when the boatlift ends.

Meanwhile, increasing incidents of larcenies and other disturbances at the Arkansas Army camp housing 19,000 Cuban refugees required flying in 127 Spanish-speaking members of the Puerto Rican National Guard, officials said.

Lt. Col. A. T. Brainerd listed five larcenies Tuesday night, and an incident in which up to 40 refugees attempted to leave the camp after the 8 p.m. curfew.

In addition to the national guardsmen, state police have been made available to help keep the Cubans on the post, one of four refugee centers in the country.