The Northrop Corp. yesterday labeled as "unadulterated nonsense" claims by three former or current employes that the guidance system for the MX nuclear missile was made so poorly that the missile could never hit a target.

David N. Ferguson, group vice president of Northrop's Electronics Systems Group, which makes the guidance unit for the MX "Peacekeeper" missile, told the House Armed Services Committee that "the allegations" made before that panel last week "are off target, not the Peacekeeper.

"To respond as gently as I know how," he said of last week's assertion that an MX was as likely to hit Washington as Moscow, "that's unadulterated nonsense. The performance and reliability" of the guidance unit known as the IMU -- inertial measurement unit -- "has been proven throughout the demanding testing and test-flight regime of the Air Force."

Although Air Force officials have said the MX has had 17 successful flight tests, they acknowledged in earlier hearings that Northrop has fallen so far behind in its delivery of guidance units that seven of the 21 MX missiles that were supposed to be operational by now cannot be used. They are standing in former Minuteman silos at the Francis E. Warren Air Force Base at Cheyenne, Wyo., without guidance units.

"They're unguided missiles," said Committee Chairman Les Aspin (D-Wis.), decrying the situation.

The Air Force said it has units being used for training that could be placed inside the seven incomplete MX missiles in an emergency. Ferguson said Northrop has instituted a "recovery program" to speed deliveries and close the existing guidance gap. He added that each of the guidance systems in the 14 MX missiles that are deployed "is never turned off. It is running and ready all the time. It is running now."

Noting that Aspin has said the key question is whether the MX, the centerpiece of President Reagan's strategic program, can be relied upon, Ferguson told the committee: "The answer is, absolutely."