Less than four months after receiving an 8 percent rate increase the Washington Gas Light Co. asked the D.C. Public Service Commission yesterday for an 18.28 percent rise which would bring in $17.8 million.

The company said yesterday's request was necessary because the commission took 20 months to grant its last permanent increase, and by that time the figures used in the decision were outdated.

"In serving our customers, Washington Gas can't meet today's requirements and prepare for tomorrow's with rates based on yesterday's costs," said WGL President Donald J. Heim.

The increase would raise the average residential heating customer's bill by $8.74 a month, from $43.85 to $52.59, a company spokesman said. A non-heating customer's bill would rise by $4.91 a month, from $15.01 to $19.92 the spokesman said.

"That's even more than I thought they'd file for," D.C. Peoples Counsel Brian Lederer said. "We're going to take a look at that company to see what they're doing to stabilize their earnings."

Lederer, the official foe of utility companies, said that as a business, WGL should find more imaginative ways of managing its affairs other than relying on residential customers and asking for rate increases. The residential gas market "is not going anywhere," Lederer said. "They have to learn to manage themselves."

The company said it requested higher rates because of increased costs of labor, materials and supplies. The higher rates would enable the company to finance routine replacements and additions to the gas system at reasonable interest rates, the company said.

WGL said that its rate of return on operations in the city is only 2.7 percent.The rate of return with the new rate request would be 10.62 percent, the spokesman said. The company's preoccupation with achieving a rate of return exceeding about 9 percent, the rate authorized by the Public Service Commission, is "a welfare mentality," Lederer said. The company should not expect a guaranteed income, he added.

When its last rate increase was filed in 1977, WGL requested a 12.56 percent hike to bring in new revenues of $11 million. That request, granted in March, raises the average residential heating customer's bill by about $3 a month.

More recently, the company asked for a $6.1 million interim raise. If granted, it would be deducted from yesterday's requested amount, the spokesman said.

For a 12-month period ended May 31, net income for WGL declined to $14.16 million ($2.58 a share) from $16.89 million ($3.19 a share) in the comparable previous months. Revenues also declined by $8 million to $351 million, as warmer than normal weather reduced natural gas sales over the past winter.