The Justice Department will consider lenient treatment of corporations that voluntarily come forward and expose price-fixing conspiracies or other antitrust violations, a top official announced yesterday.

John H. Shenefield, assistant attorney general in charge of the Antitrust Division, said he hoped the new policy would induce some corporations and individuals to make "a clean breast" of their complicity in illegal activities rather than face the severe criminal penalties possible if their wrongdoing is detected and prosecuted by the government.

Shenefield's remarks came in a speech prepared for delivery in Chicago to the annual Corporate Counsel Institute, attended by lawyers who Shenefield said would be in a position to find out about possible violations early-on and were likely to be involved in the corporate decisions on whether to make disclosures.

Shenefield also outlined the benefits of coming forward - before being caught - in referring to a corporation that several months ago revealed its involvement and that of some of its officials in a previously undetected price-fixing scheme.

"The appearance at our door of a corporation wishing to confess to something we don't know about is for us a novel occurence," he said. He noted that the step was taken at the risk of both indictment and substantial liability to injured parties, and without "any apparent prospect" that the government would uncover the conspiracy.

Cooperation by the firm - not named by Shenefield but identified by other Justice sources as Titanium Metals Corp. of America - led to the indictments of four other corporations and five individuals last week. Titanium Metal was named as a co-conspirator but was not indicted; it was named as a defendant in a companion civil case.

[Although the practice isn't common, Titanium Metals wasn't the first firm ever to come forward. Last year, for instance, Singer Co. informed the division of the results of an internal investigation that disclosed potential antitrust violations.]

"Public prosecutors traditionally have exercised discretion in granting and recommending leniency toward potential and actual defendants who cooperate with the government," Shenefield. Such cooperation can save the government time and money and improve the chances of convicting the guilty and eradicating the illegal conduct.

In the case of antitrust enforcement, encouraging cooperation may results in savings of millions of dollars to consumers, he added.

However, leniency won't be automatic, Shenefield noted. Only the first corporation to come forward in a violation will be considered for leniency, he said, and the division will consider other factors such as whether the corporation that discovered illegal activities took prompt and effective action to end its part in the conspiracy.

Although he admintted he didn't expect a "stampede of confessing corporations," he admonished firms to "wipe out past violations, get into full compliance with the law - and stay there."

On related matters, Shenefield said:

Prosecution results for fiscal 1978 showed a sharp movement upward in severity of sentences, indicating the courts heard the message Congress sent by changing antitrust violations from misdemeanors to felonies.

Total corporate fines in 1978 were $11 million compared with $2.6 million in 1977; total individual fines were $1 million compared with $755,000 the year before; total days in jail totaled 2,921 for 29 individuals, almost double the 1,561 days for 24 individuals spent in 1977.

The premerger notification program, under which corporations tell the government in advance of large mergers, will be "procedural" except for those 'who choose tthe obstructionist route." Those who don't respond to the government's request for information affirmatively may find it "expensive and burdensome."

The plan has been in effect since Sept. 5, and Shenefield said the government already has been notified of 120 proposed mergers. As a result, the division has begun 18 formal investigations and the Federal Trade Commission has begun 13.