Depressed profits from coal mining operations caused a 5 percent decline in first-quarter profits for Pargas Inc., Chairman William Hill told the company's stock-holders yesterday.

At the annual meeting in suburban Waldorf, where Pargas is based, Hill said profits in the quarter totaled $3.3 million (90 cents a share) compared with $3.4 million (95 cents) in the same period last year. Revenues rose 12 percent to $53 million.

Hill noted that the results were the second highest for a first quarter in Pargas history and said sale of propane resulted in the highest profits from that line of business for any quarter in history.

But cold weather impeded coal mining operations, halted some rail shipments, prevent barge loadings and led to higher expenses. Although mines owned by Pargas are non-union, workers stayed off their jobs for a month during the 110-day nationwide strike.

Losses during that 30-day period together with "unfavorble operating conditions" in January and March produced a net loss of 20 cents a share from the Pargas coal business or the quarter, Hill said.

Despite the loss, coal operations have picked up in April and management expects "good results" for the full year. Coupled with an expected increase in demand for propane, pargas earnings should be at record levels for 1978, he added.

Directors yesterday approved a quarterly divided of 26 1/2 cents a share, payable May 26 to owners of record May 12.

Washington Gas Light Co. reported yesterday that profits increased in the first quarter to $19.5 million ($4.30 a share) compared with $18.9 million ($4.22) in the same period last year. Revenues rose to $160 million from $132 million.

Schwartz Brothers Inc., a Washington retailer and wholesaler of music merchandise and owner of the 17 Harmony Hut stores, reported record sales and profits for the year ended Jan. 31. Net income was $551,637 (73 cents a share) compared with $349,636 (46 cents) as sales increased to $29 million from $25 million.

Directors of Schwartz voted yesterday to declare an initial 10-cents-per-share divided on common stock, payable May 25 to owners of record May 10.