C3 Inc., a Reston-based computer systems firm, said its earnings for the year ended March 31 fell 80 percent, primarily because of a $6.6 million writedown of obsolete inventory.

The company's revenue, however, rose 18 percent to $72.4 million from $61.1 million.

C3 said it earned $873,000 (9 cents a share) in the year, off from $4.3 million (47 cents) in the previous year. The $6.6 million inventory writedown was partially offset by a $1.3 million gain resulting from the sale and leaseback of the firm's corporate headquarters.

For the fourth quarter ended March 31, the inventory writedown gave the company a $2.6 million loss, compared with a $438,000 loss the previous year. Revenue in the quarter rose 24 percent, however, to $18.8 million from $15.1 million.

* Crown Books Corp. reported a 5 percent increase in profits for its first quarter that ended April 30. Net earnings for the quarter were $1.338 million (17 cents a share), up from $1.274 million (16 cents) for the same period in the previous year.

Sales rose by 13 percent to $25.9 million from $22.9 million the previous year.

* Trak Auto Corp. said its income decreased 55 percent in the fiscal first quarter because of losses from the auto parts retailer's Trak Auto West affiliate and reduced profits at its Trak Auto East subsidiary.

Trak Auto West, of which Landover-based Trak Auto Corp. owns 50 percent, lost $1.8 million in the quarter, compared with a $2.1 million loss in the same quarter a year ago. Meanwhile, wholly owned Trak Auto East was earning $1.3 million, down nearly one-third from profits of $1.9 million a year earlier.

The company attributed the poor results to high costs of Trak Auto West's expansion in the highly competitive Los Angeles market, in which it has 58 stores, seven of them opened in the past four months. Trak Auto East operates 102 stores in the Washington, Richmond and Chicago areas.

The combination of Trak Auto's half-share of the Trak Auto West results and the Trak Auto East results gave the company income of $395,000 (7 cents) in the quarter, off from $873,000 (15 cents) a year earlier.