The Washington Gas Light Co. applied yesterday for a $3.6 million, 2.41 percent rate increase in Maryland that would raise the bill of the average residential customer with gas heat in his home by about $1 a month. The company has 228,000 Maryland customers.

WGL's last Maryland rate increase for $2.8 million was granted by the Maryland Public Service Commission 10 months ago. The company has received increases totaling $27.5 million in four rate cases during the past five years.

In its current increase request as in the request that led to the last increase granted the company seeks to earn its authorized rate of return on investment without seeking to raise that percentage of return or to alter any accounting rules.

The authorized rate of return on investment is that portion of the money that the company earns by selling gas that it needs to pay interest and dividends to investors in its stocks and bonds.

When the company fails to earn that rate of return - 9.25 per cent in Maryland - it may file a rate increase request under a law that went into effect in 1976. Such a filing avoids the complexities of a major rate increase case, and the PSC must make a decision within 90 days.

John Keane, the Maryland People's Counsel who represents the public in utility cases, said he may be able to argue for limiting the requested increase on grounds that the law allows the company the "opportunity" to earn its authorized rate of return, but does not guaranttee it.

"I think there's room to make that argument," said Keane. "There's some latitude in there."

Earlier this month Virginia's State Corporation Commission approved an 8.2 percent increase for WGL's 167,000 Virginia customers that will raise the monthly bill in the average home by about $4. WGL is also seeking a 12.5 per cent rate increase in the District of Columbia, where it has 150,000 customers.

A company news release yesterday said the requested increase would raise monthly bill of the average Maryland residential heating customer by $97, from $39.80 to $40.77, and that of the average non-heating customer by $29, from $12.13 to $12.42.