U.S. economic growth could ease by the middle of this year, according to the Economic Cycle Research Institute's weekly leading index.

"The decline in [weekly leading index] growth to a 30-week low underscores our view that U.S. economic growth will start easing by mid-year," said Lakshman Achuthan, managing director of the institute.

In the weekly period ended Feb. 26, the weekly leading index level rose to 129.8 from the prior period's reading of 128.4. However, the index's growth rate fell to 13.7% from 14.0%.

The growth rate and level can move in opposite directions because the growth rate is derived from a four-week average of the level that is compared against the previous year's average.