Washington Gas Light Co., whose "nonessential human needs" customers were ordered last night to cut back thermostats as far as possible, reported a surge in fourth-quarter 1976 profits because of cold weather that resulted in higher natural gas consumption.

Profits from operations in the October-November quarter totaled $6.8 million ($1.40 a share) compared with a loss in the 1975 period of $1.6 million, when the weather was abnormally mild. Revenues rose to $83 million from $57 million.

The gas company also benefitted from a $1.39 million one-time gain in the recent quarter, equal to 33 cents a share, from settlement of a suit filed against Atlantic Richfield Co. and bringing final net income for the recent quarter to $8.2 million ($1.73).

Braced with the fourth-quarter rebound, Washington Gas earnings for the full year also increased to $17.2 million ($3.30 a share) compared with $10.8 million ($1.96) in 1975, which was one in a series of depressed years for the local utility.

The 1976 profits include the Arco settlement's one-time gain while the 1975 results reflected a one-time gain of $2 million (47 cents) related to an accounting change.

Washington Gas revenues in 1776 were $270 million, a gain of $45 million from the previous year.

A statement from the gas company attributed the "considerable improvement" for 1976 primarily to the colder weather in the final months of the year. Overall, heating months last year were 13 per cent colder than in 1975, the film reported. Rate increases approved late in the year "were only a minor contributing factor," WGL added.

At the end of 1976, Washington Gas and subsidiaries had 545,263 meters in service compared with 547,518 a year earlier.

American Realty Trust, a real estate investment trust in Arlington, reported a net loss of $3.8 million in the year ended Sept. 30 compared with a loss in the previous year of 2.8 million. Revenues rose to $5.4 million from $3.6 million.

ART added $2.9 million to reserves for possible loan losses in the recent year, mainly related to its investment in the Representative condominium apartment property in Arlington County.

The trust said projected cash requirements for the new fiscal year are in excess of available resources and said it "hoped to bridge the projected gap through successful renegotiation of its outstanding debt." For the second year, ART's outside auditing firm declined to express an opinion on the statements because of "material uncertainties related to financing and other contingencies."