Penril Corp. of Rockville reported lower earnings for the second quarter ended Jan. 31 although revenues reached record levels.

Penril said net income for the quarter was $577,000 (29 cents a share) compared with $695,000 (35 cents) in the comparable period of 1981. Revenue increased from $9.8 million a year ago to $10.4 million in the most recent quarter.

Penril said earnings for the quarter were affected by unfavorable economic conditions and tight consumer credit, which reduced revenues in its consumer audio equipment division.

Net earnings also declined in the first six months, falling from $1.2 million (61 cents) in the first half last year to $808,000 (41 cents). Sales rose from $18.9 million to $19 million.

In another development reported yesterday, Penril said its Electro-Metrics division has been awarded a $1.58 million contract to provide radio interference measuring devices for the Army.

Penril designs and manufactures a diversified line of high technology and other electronic equipment.

Survival Technology, a Bethesda-based developer and manufacturer of medical devices, said unaudited results for the second quarter show net income was $76,700 (three cents), compared with $40,500 (two cents) last year.

Sales for the quarter totaled $4.7 million compared with $3.9 million in the same period last year.

For the six months, net income was $285,000 (11 cents) compared with $221,800 (nine cents). Sales rose from $8 million in the first six months last year to $9.6 million.

The National Press Building Corp. reported record income in 1981 but net earnings declined, stockholders were told at the corporation's annual meeting yesterday.

The corporation said net income was $102,634 compared with $183,795 in 1980. William D. Hickman, president of the corporation, said a deferred compensation expense was responsible for the earnings decline.

Hickman said total income for 1981 was $3.6 million, compared with $3.4 million.

Stockholders were told that they can expect an interruption in a string of profitable years in 1982 as additional tenants are displaced by extensive reconstruction at the corporation's downtown office building.