Hechinger Co. yesterday reported its 40th consecutive quarter of increased profits, with net earnings of $6.131 million (34 cents a share) in the fourth quarter. That was a 19 percent increase from the $5.144 million (28 cents) it earned in the same quarter last year.

The Landover-based company, which operates 45 do-it-youself home centers, also said that earnings for the year, at $20.923 million ($1.15), were 29 percent higher than the $16.243 million (90 cents) recorded in 1983. Hechinger's fiscal year, which ended Feb. 2, was 53 weeks, and the fourth quarter was 14 weeks compared with 13 weeks in the fourth quarter of fiscal 1983.

Revenue from 1984 operations was $405.077 million, up 31 percent from $309.499 million in 1983. Fourth-quarter revenue was $102.415 million, up 30 percent from $78.977 million in the last quarter of 1983.

* Penril Corp. of Rockville said yesterday that earnings for the quarter ending Jan. 31 were up 35 percent from the same quarter the previous year, from $591,000 (29 cents) to $799,000 (37 cents). Penril, a manufacturer of computer data communications equipment, electronic scientific test instruments and audio equipment, said its revenue for the latest quarter was $19.170 million, up 19 percent from $16.128 million in the same quarter the year before.

That increase includes $3.787 million in revenue from Concord Systems Inc., which Penril acquired on Dec. 31.