BOISE, Idaho (AP) _ Boise Cascade Corp. on Thursday reported its 13th consecutive quarterly loss, saying it had a deficit of $37.6 million in the first three months of 1994.

The wood product company's loss of $1.35 per share in the three months ended March 31 was a sharp deterioration from losses of $12.1 million, or 56 cents per share, in the same period a year earlier. Sales rose to $1.01 billion from $984 million.

First-quarter performance contradicted predictions in January by chairman John Fery that the worst of the cyclical downturn in the paper products industry was past.

''Contrary to generally held expectations, paper prices fell in the first quarter of 1994, particularly in grades most important to Boise Cascade,'' the company said Thursday.

Aggravating the price decline were increased manufacturing costs due to severe winter weather, maintenance and ''related operating difficulties at some facilities.''

Paper products account for nearly half of Boise Cascade's sales.

Rising pulp and containerboard prices during the quarter were not enough to offset a decline in the price of newsprint and a 5 percent drop in average prices for coated and uncoated white paper, the company said.

Boise Cascade reported only a slight improvement in operating profits from office products, which account for less than 20 percent of total sales.

Operating income from building products, which account for about a third of sales, fell 77 percent from the first quarter of 1993 as timber prices rose on tight suply and bad weather limited winter construction.

The company's stock was down 25 cents at $23.25 in late-afternoon trading on the New York Stock Exchange.