The new owner of U.S. News & World Report, Mortimer B. Zuckerman, yesterday assured employes that he intends to defend them vigorously against a lawsuit by former employes seeking a share of the $176.3 million he paid for the magazine.

In a seven-page memo issued yesterday, Zuckerman's newly appointed executives told the staff that a recent motion filed in court by his lawyers in no way represents "a reduction in the vigor with which the company intends to defend the unmeritorious lawsuit brought by former employes."

The memo said that Zuckerman is not trying to escape any of the liabilities he assumed when he purchased the magazine a little more than two weeks ago.

The former employes claim in their lawsuit that they are entitled to part of the money to be received from the sale of the employe-owned magazine. U.S. News employes earned stock in the publication and were required to sell their stock back to the company when they retired. The retired workers contend they did not get a fair price for stock because the company's management deliberately undervalued it.

The memo from Fred Drasner, the company's new vice chairman, and Jim Glassman, the new executive vice president, was issued in answer to questions raised by some company employes late last week after they received a copy of a legal document filed in the lawsuit by Zuckerman's lawyers.

Many employes charged that the documents represented an attempt by Zuckerman to reduce the liability for the suit that he had agreed to assume when he purchased the magazine.

In the documents, Zuckerman supported a move by the former employes to include the employes' profit-sharing trust as a defendant in the lawsuit. The trust contains about $135 million of undistributed proceeds from the sale. If the trust is included in the lawsuit, the amount of money each individual would receive from the sale could be reduced. Up until two weeks ago, the former employes had not tried to make the trust part of their lawsuit.

Zuckerman added in an interview about the memo that he wants to get the disputed funds distributed to current employes as quickly as possible.

Employes charged that, when Zuckerman purchased the magazine, they were told by company officials that he agreed to assume any liability for damages from the lawsuit if they exceeded $10 million. The first $10 million was to be paid from the $176.3 million purchase price and, as a result, has been set aside in an employe contingency fund.

The memo said that Zuckerman has not changed his agreement: "Mr. Zuckerman agreed to assume, has assumed, and continues to be responsible for, the unlimited liabilities of the company in excess of the contingency fund."

However, the statement added, "The agreement did not require Mr. Zuckerman to assume any potential liability or expense of the profit-sharing plan . . ."

Because the former employes charge that they did not receive all of the benefits to which they were entitled as part of the profit sharing plan, "the plan was required, as a matter of law, to be a defendant," the memo said.