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Foreshadowing strong economic growth into the summer, the composite index of leading indicators rose 0.7 percent in February, the 18th consecutive advance, the Commerce Department reported Thursday.

The index of 11 indicators is at 165.9; its 1967 base level was 100. Growth is moving faster than in any of the other post-World War II recoveries. Another sign of the fast pace was Thursday's report that sales of new houses jumped 7.8 percent in February. Housing is a key industry in the economy.

Economists expect expansion to continue but to slow later this year. Whether that will prevent a credit crunch is an open question and depends as much on the strength of the economy as on the federal budget deficit.

''We still see continued economic growth through the spring quarter,'' says economist Sandra Shaber of Chase Econometrics in Bala-Cynwyd, Pa. ''The real risks of higher interest rates will come toward the end of the year and early ' 85.''

How reliable is the index? Dr. Shaber says she views it with ''a jaundiced eye'' and adds: ''Most economists tend to agree with the index when they say growth and the index does, too.''