Santiago Carrillo, secretary general of the Spanish Communist party, will speak tonight at 8 p.m. at Science Center B.

Carrillo arrived here last night. He will spend the day at Harvard visiting classes and attending functions planned by the Center for European Studies, which invited him to speak here earlier this fall, Peter M. Lange, associate professor of Government, said yesterday.

An advocate of Eurocommunism, Carrillo's speech probably will focus on his belief that a country can achieve socialism through parliamentary institutions while maintaining its independence from the Soviet Union.

Moscow has sharply criticized Carrillo in recent years for his maverick beliefs and his assertion of the independence of European Communist parties from Soviet hegemony.

Professors and graduate students from local universities will dine with Carrillo at the Center for European Studies before this evening's speech, Lange said. Carrillo will hold a press conference at the Center at 4 p.m. today, he added.

Tomorrow, a smaller group of Eurocommunism specialists will join Carrillo for lunch before he leaves Harvard, Lange said. Lange would not say what classes Carrillo planned to attend today.

The International Relations Council helped the Center plan fro Carrillo's visit and is co-sponsoring tonight's speech.