Three Harvard professors are among 91 scientists nationwide who received a $25,000 grant from the Alfred P. Sloan Foundation for 1989, selection committee members said yesterday.

Associate Professor of Economics and Government Alberto F. Alesina, Associate Professor of Mathematics Zhihong Xia, and Associate Professor of Physics Cumrun Vafa will each be granted $25,000 in the next two years through a Sloan Research Fellowship to aid them in their research.

The fellowships, established in 1955 by the New York state foundation, are given to scientists in the early stages of their careers in economics, mathematics, physics, chemistry and neuroscience. Eleven Nobel laureates are among the nearly 2500 fellowship recipients.

Although the University will administer the money for Alesina, Xia and Vafa, each fellow has "pretty much complete freedom" in using the research funds, Professor of Astronomy and Physics William H. Press said yesterday.

Press, a member of the Sloan grant selection committee, said fellowship funds can be used for equipment, technical assistance, professional assistance, professional travel, trainee support or other activities directly related to the fellows' research.

Alesina, a researcher who aims to integrate the study of political science and macroeconomics particularly in monetary and fiscal policy, said he plans to use the fellowship for office expenses and to purchase computer equipment.

Xia, whose work involves applying mathematical principles to the motions of astronomical bodies, said he may use the Sloan funds to relieve teaching pressures, attend academic conferences and purchase equipment.

Vafa could not be reached for comment yesterday. His research concerns the "super string theory" in physics, which was developed to help provide a single equation for physicists to interpret the four basic forces that appear in nature.

"Vafa richly deserves the award because he is one of the leaders in his field at a young age," said Donner Professor of Science Sidney R. Coleman, who won the fellowship 28 years ago.