Washington Gas Light Co. yesterday said its 1979 profits increased from $13.5 million ($2.44 a share) to $14.3 million ($2.65), not counting a change in the company's accounting methods.

The accounting change added $4.4 million, or $1.01 per share of common stock, to Washington Gas earnings, raising net income to $18.7 million and earnings per common share to $3.66.

Higher gas rates and increases in gas sold to special contract customers boosted the company's income. The gains were partially offset by warmer weather during the heating season; November and December last year were the warmest on record.

Washington Gas revenues climbed to $384.9 million from $352.9 million for the 12-month period, and gas sales increased by 35.5 million therms to 1,154 billion. The company picked up 3,170 new customers during the year.

Pargas, a Waldorf, Md., distributor of liquified petroleum and other gases, reported its 1979 net income nearly tripled, jumping from $4.2 million to just over $12 million. After deducting dividends on preferred stock, the earnings were equivalent to $3.30 a share of common stock, up from $1.12.

For the final quarter of the year, Pargas earned $4.3 million ($1.19), up from $2.5 million (71 cents).

General Kinetics Inc., of Rockville reporting results for a strike-impacted six months ended Nov. 30, posted a net loss of $11,446 on sales of $1.2 million compared with earnings a year ago of $91.262 (12 cents a share) and sales of $1.4 million.

The company's production workers in Johnston, Pa., were on strike for 16 weeks during the period. GKI produces magnetic tape maintenance equipment and also services such facilities.

Testdata Systems Corp., a McLean company that supplies computer management systems, made a preliminary report that its revenues will top $5 million for the fourth quarter and earnings will be between 35 cents and 40 cents a share.

President Thomas Stone said the strong quarter will enable the company to "about break even" for the year.