The Exxon Corp. has overcharged buyers of natural gas liquids by more then $316 million since August 1973, according to a suit filed against the company yesterday by the federal government.

The Department of Energy suit, filed in U.S. District Court here, asked that Exxon be ordered to repay the alleged $316 million overcharge plus interest to the federal government, which would accept claims for restitution from Exxon customers.

In a statement released late yesterday, Exxon said its pricing actions concerning natural gas liquids "were in complete compliance with the applicable regulations." The company said it would contest the suit.

DOE said the suit arose out of a "comprehensive audit conducted by DOE's office of special counsel," and that it represents the largest single enforcement action ever filed in connection with the government's investigation of oil industry pricing regulations.

That investigation has uncovered an alleged $1.7 billion in overcharges by several oil companies in various areas of pricing.

Some $600 million of that total has been charged against Exxon, DOE sources said, in the form of court actions and administrative levies, including notices of probable violation.

In yesterday's suit, the government alleges that Exxon improperly over- priced the cost of natural gas liquids, which are used for such products as propane and butane, and as feeder stock in the gasoline refining process.

The federal regulation in question ordered oil companies to freeze the price of natural gas liquid products at the May 1973 level, and allowed increases only when the companies could show increases in costs of production.

The government alleges that when Exxon was buying natural gas liquids from its affiliated companies it inflated the value of those liquids.

According to the DOE filing, Exxon set the price of the liquid it was buying from its own companies at the amount it claimed it cost to buy those liquids on the open market.

But, the government alleges, those prices were set too high.DOE says that Exxon also was buying some natural gas liquids from non-company sources and paying less than it claimed it would have had to pay for its own natural gas.

The government suit also asks the court to enjoin Exxon from future overpricing.

DOE proposes to set up an administrative claims procedure under which companies and individuals can claim they were victims of the alleged overpricing and collect restitution. Any remaining moneies would go to the U.S. treasury, according to DOE's plan.

Yesterday's suit was an outgrowth of an action by DOE in March when it issued a notice of probable violation against Exxon, estimating that the company overcharged purchasers of natural gas liquids by $145 million between August 1973 and December 1976. BUt after Exxon replied to the notice and DOE updated the alleged overcharges to include 1977, the government decided to proceed with court action.

Exxon claims it has raised this and other pricing issues in court.

"More than three years ago Exxon tried to resolve the natural gas liquids pricing question with the governmental administratively," Exxon senior vice president O. L. Luper said yesterday. "That effort proved futile and we brought suit in Dallas." That suit is unresolved.

"The issue that has been before the court should be resolved in Dallas rather than delay a decision any longer by legal maneuvering which seeks to get another court to start the case again from scratch," Luper said.

Much of the renewed federal investigation of oil overpricing, conducted by DOE special counsel Paul Bloom, has been mixed in legal battles in which the the government is seeking to have the cases tried in Washington, while the industry is trying to make Texas courts the forum.

An earlier $185 million suit against Exxon for crude-oil overpricing which was filed in Washington this year, is in the discovery stage.