The Energy Department yesterday accused seven oil companies of over-charging customers more than $1 billion from 1973 through 1976.

The latest action brings the total amount of overcharges alleged by DOE against the top 15 oil companies in the last two years to almost $10 billion.

Sources in the department's Office of Special Counsel said yesterday's allegation of 40 separate violations of federal pricing regulations represents the last major charges that will be brought against the 15 companies.

DOE says it will now proceed with the second phase of its investigation concentration on comprehensive audits of the 19 next largest oil firms.

Yesterday's action were filed in the form of 40 Notices of Probable Violation against Shell ($370 million), Conoco ($168 million), Arco ($280 million), Marathon ($68 million), Sohio ($154 million), Chevron ($20 million) and Texas Texaco ($31 million).

Only about one-tenth of the actions brought by DOE in this controversial investigation have been resolved. In those cases, representing about $1 billion of the alleged overcharges, the companies agreed to refund about $700 million.

Two companies have settlked completely. Phillips Petroleum, accused of $234 million in overcharges, has agreed to pay back $200 million, and Cities Service consented to refund about $200 million to settle allegations of $292 million in overcharges.

Most of DOE's allegations have been challenged by the industry, which has charged the department with conducting a war against it in the press. w

There has been an almost continuous series of headlines heralding billions of dollars of alleged over-charges, the industry argues. And, it says, many of the articles about those overcharges were published before the companies were told they were being charged.

DOE's allegations center around industry compliance with the complex set of federal pricing and allocation regulations developed during and after the 1973 oil embargo.

In statements yesterday, Conoco and Sohio reiterated industry charges that DOE's allegations are unfair.

In a statement from its Cleveland headquarters, Sohio said the charges against it were "grossly exaggerated and intended to create sensational news." It added that it would challenge then in court.

In Houston, Bruce F. McCall, Conoco's vice president for U.S. Marketing, called the charges against that company a "patchwork of assumptions, guesses and projections," and said Conoco "has tried conscientiously to follow the DOW's very complex regulations and is convinced it has done this correctly."

The nearly final tally of the initial DOE Investigation shows Texaco in the top spot with $1.371 billion in alleged overcharges. Exxon and Gulf had $1.3 billion each, according to DOE.

Other totals included: Mobil ($979.5 million), Hess ($915 million), Shell ($872.7 million), Sun ($630.1 million) Arco ($525.2 million), Chevron ($395.7 million), Sophio ($353.1 million), Conoco ($319.8 million), Amoco ($144 million) and Marathon ($136.9 million).

For the most part, the charges involve pricing practices. DOE has accused several companies, for example, of improperly labeling "old oil" -- which was still under price regulation -- as "new oil" and charging customers the higher price allowed for it.

In othercases, DOE alleges, companies misclassified customers, charging them price that were restricted to other classes of customers -- smaller buyers, for example.