WASHINGTON — Businesses added to their stockpiles in March by the smallest amount in a year, another indication of a weakening economy.

The Commerce Department reported Tuesday that business inventories edged up a tiny 0.1 percent in March, the smallest advance since inventories were basically flat in March 2007.

The small rise was below the 0.4 percent increase that many economists were expecting. It indicated that businesses are holding back on adding to their stockpiles in the face of slowing demand.

If businesses get serious about restraining inventories, that would add another drag to economic growth, resulting in cutbacks in production.

The 0.1 percent rise in inventories held on shelves and backlots in March followed a much bigger 0.5 percent increase in March.

The small amount of strength in March came from a 0.9 percent gain in inventories held by manufacturers. Inventories held by retailers dropped by 0.5 percent and wholesale inventories were down 0.1 percent.