The Reagan administration yesterday hailed the first year of its Caribbean Basin Initiative as a success, but a leader in the region said more aid is needed and that small island nations should be separated in the program from the larger mainland states.

Prime Minister Eugenia Charles of Dominica said small island nations such as hers need extra aid to build up their infrastructure so they can take advantage of the potential of the CBI to increase investment in the region. She called lumping the small nations in the same program with larger mainland countries such as El Salvador, Costa Rica and Guatemala "a great disservice to the island."

Nonetheless, administration officials said the program has resulted in increased investment in the region, citing 250 projects that created 27,500 new jobs in the 29 nations taking part.

Kenn George, director general of the Commerce Department U.S. and Foreign Commercial Service, said investment in the CBI's first year totaled $153 million.

Charles spoke at a luncheon celebrating the first year of the CBI, the Reagan administration program that started Jan. 1, 1984, to improve economic conditions in the Caribbean Basin through private-sector trade and investment as well as government aid. George made his comments at a press briefing by U.S. government officials that followed the luncheon.

Commerce Deputy Secretary Clarence Brown said the new jobs and added investment show the CBI program succeeded in its first year and is growing stronger this year.

"The companies who today are showing interest in the region tend to be larger, more financially secure and more serious than was previously the case," Brown said. "These companies are realizing that CBI is not going to fade away like previous 'new initiatives' to assist the region."

U.S. imports from CBI countries increased 17 percent to $3.8 billion last year, while American exports jumped 6 percent, to $5.4 billion.