Robert M. Solow, an economist at the Massachusetts Institute of Technology, yesterday was awarded the Nobel Prize for economics for his work in determining the sources of economic growth.

Solow, 63, is a witty, engaging man held in unusually high regard by other economists not only for his analytic and research abilities, but also for keeping that research relevant to the real economic world.

The work cited by the Nobel committee for the award was done in the mid-1950s. Solow studied the period 1909-1949 in the United States and concluded that the bulk of the increase in the economy's output, other than that due simply to having more people at work as the population grew, was the result of technological advances.

Assar Lindbeck, president of the Nobel committee, said that by the 1960s, Solow's work had influenced countries to concentrate more resources on universities and research. The statement said Solow's "theoretical model had an enormous impact on economic analysis."

Members of the five-man committee also described Solow as "easy-going and humorous" and "a very good teacher." Indeed, when his colleagues awarded him M.I.T.'s Faculty Achievement Award in 1978, they said he was especially valuable to the school because he divided his time among his students and his research.

Solow continues to deliver introductory economics lectures at the school, whose economics faculty is regarded as among the best in the nation.

Solow, who was born in Brooklyn, is the 15th American to win the Nobel Memorial Prize in Economic Sciences, which was established in 1968 by the Bank of Sweden. The winner last year was James M. Buchanan of George Mason University for his use of economic analysis to the way in which public policy decisions are made. The prize carries an award worth about $340,000.

Charles L. Schultze of the Brookings Institution, a former chairman of the president's Council of Economic Advisers, said Solow did considerably more than identify a key source of economic growth in the mid-1950s. He also found a way to merge the theories of John Maynard Keynes and those of earlier classical economists to explain why small shifts in investment did not necessarily produce recessions, as the developing Keynesian theory indicated it would.

"Part of what he developed was the possibility of a slower adjustment process, that you could have varying rates of growth without necessarily having a recession," explained Schultze.

One reason that Solow's work on economic growth is so highly regarded is that, unlike some competing theories, it has stood the test of time. Later work of other economists has confirmed his conclusions, and they remain an essential part of modern mathematical models of how national economies grow.

Schultze said he has continued to move into new areas of research, such as the way in which union and management bargaining can produce what economists call "sticky" wages -- that is, wages that do not adjust promptly to changed economic circumstances. Higher unemployment can be a by-product of sticky wages.

"He has been simultaneously very good and very up to date, and when necessary very mathematical," Schultze said. "But he has also stayed in touch with reality. He's not the only one to manage that, but he is one of the most prominent to do it."

And Schultze added, "If it is possible to get an oak leaf cluster on your Nobel for humor, he ought to get it."

Solow, who loves sailing and retreats each summer to Martha's Vineyard, is in constant demand at economic conferences, often to moderate panels or provide a summary of what has transpired. He can leave an audience in stitches while giving a pithy summation of diverse and often arcane economic views.

"My friends have been telling me for the last couple of years that I must be in the running for this," Solow said yesterday. "It's embarrassing to be told that all the time, so I guess I knew that, but {the award} came as a complete surprise."

Asked about the plunge in stock prices this week, Solow blamed "the combination of the balance-of-payments deficit and the federal budget deficit, which has put our country in the position of financing a consumption boom by borrowing from foreigners ... We're going to be a number of years digging ourselves out of a hole that we dug for ourselves over the past six or seven years."

Solow was a senior economist at the three-man Council of Economic Advisers during the Kennedy administration, but was generally regarded as really being a fourth member of the council, Schultze said. He is also a former president of the American Economic Association.