Washington Gas Light Co. yesterday reported a decline in profits for 1978 despite a $32.4 million increase in revenues last year over the previous year.

Net income declined from $12.2 million in 1977 to $10.9 million last year. Earnings per share of common stock fell to $2.51, down from $2.81 in 1977.

Earnings for 1977 were restated because of newly inposed standards of full cost accounting by the Securities and Exchange Commission. Those changes decreased net income by 23 cents per share in 1977.

Despite weather that was 3 percent colder during the heating months of 1978 than the previous year, earnings declined 30 cents per share.

During that same time, revenues increased from $320.6 million in 1977 to $353 million last year.

Because of the restatement of earnings, fourth-quarter figures were not available yesterday, a Washington Gas Light spokesman said.

The company cites as reasons for declining profits delay by the Public Service Commission in granting rate relief requested in July 1977 and increasing costs and eroding earnings due to inflation.

The company recently announced plans to detect and charge higher rates to customers who use electric heat pumps to cut gas consumption significantly. These customers would continue to cost the company the same amount as ever in fixed capital costs, the company explained, while significantly cutting WGL revenues.

Although revenues have increased, the number of meters in service at the end of December 1978 decreased.

In documents filed with the Maryland Public Service Commission, utility officials asked that they be allowed to require customers to notify them when they install heat pumps.

The utility wuld not apply the higher rates to customers who conserve energy by turning down their thermostats or supplementing gas heat with another energy source, officials said. The utility is only concerned that the supplement becomes a major heat source.

The Hotel Investors reported net earnings for the first quarter increased to $680,000 (43 cents per share) from $614,000 (40 cents) during the same period a year earlier.

The Chevy Chase real estate investment trust said gross income for the quarter, which ended Nov. 30, increased to $2.57 million from $2.28 million.

Chairman David Callard said the trust had agreed to reduce the interest rate on a $4.4 million loan on a Hawaiian hotel from 9 3/4 percent to 6 percent for three years, but said Hotel Investors will receive additional income if the property's income improves. He said the loss of income "will be more than offset" by gains on other properties.