Senior executives of MCI Communications Inc. said yesterday that the portions of their massive antitrust complaint against American Telephone & Telegraph Co. that were thrown out by a Federal appellate court were not essential to their case. They contended that MCI could still win the same record $1.8 billion in damages.

Though the appeals court rejected MCI's claim that AT&T engaged in predatory pricing, MCI General Counsel John Worthington said pricing was a peripheral issue.

The judges of the U.S. Court of Appeals in Chicago said in their 205-page opinion that "the predatory pricing allegations play such a significant part in MCI's case" that their dismissal requires reevaluation of the entire antitrust damage claim.

The court said the jury's award of $600 million damages--automatically trebled under federal antitrust law--had to be scrapped because it included damages based on the predatory pricing claims, which the court found invalid.

William McGowan, MCI's chairman, said the two counts on which a jury verdict in MCI's favor was reversed were "not central" to the case. What matters, he said, is that the court upheld MCI's claims on eight points. "AT&T's liability is no longer in question," he said. "It has been affirmed. What remains to be decided are the monetary damages appropriate to compensate MCI for AT&T's violations of the law."

But AT&T also claimed victory in its long, bitter struggle against its chief competitor in the long-distance telephone business. A company spokesman pointed out that of the 22 claims of illegal action made by MCI when it filed suit in 1974, all but eight have been dismissed by judges or rejected by the trial jury. Those that remain, AT&T maintains, are minor issues.

The appeals court strongly affirmed the jury's finding that AT&T acted illegally in denying the fledgling MCI access to the local telephone hookups it then needed to complete its long-distance circuits.

AT&T's stalling tactics and "bad faith negotiations," the court said, "cost MCI perhaps 1 1/2 years of time and revenue while it fought for interconnections . . . in October 1973, MCI had its terminals in place and had expended substantial amounts of capital only to have its revenue flow obstructed because of its inability to operate while AT&T denied interconnection."