U.N. Secretary General Kurt Waldheim has established a two-man panel to look into pervasive rumors that high-ranking members of his administration extorted thousands of dollars from staff members in return for promotions.

Secretariat sources maintain that at least nine and perhaps more U.N. employes had been hooked by the extortion scheme, which involved "loans" -- without collateral or interest; never repaid -- ranging from $10,000 up as high as $28,000.

The charges have caused an uproar among the staff and have focused on one top level U.N. official who remains in the secretariat but is no longer in a position to influence promotions. There are also allegations that some of his deputies were involved in the scheme, soliciting loans and taking a rake-off, or soliciting sexual favors from female employes in return for promotions.

The U.N. staff union had asked for a full-scale investigation of the charges by an independent panel, and written guarantees of full immunity for secretariat employes who come forward to testify.

Waldheim's response was, in typical U.N. fashion, to agree halfway to both demands.

"The Secretary General felt that an investigation could not be initiated unless evidence was presented," said the U.N. spokesman today.

"So far, neither he nor any members of the administration have received evidence of wrongdoing."

As an interim step, the United Nations announced, the two-man panel will "receive and examine evidence to determine if there are sufficient grounds to justify a broader investigation."

The spokesman, Rudolph Stajduhar, added that Waldheim "has given assurances that staff members who wish to bring complaints will not suffer consequences from anyone in the secretariat" -- but the immunity will not extend to any wrongdoing by the claimants, such as payments for unmerited promotions.

Lowell Flanders, the staff union president, expressed his disappointment at the lack of full immunity, but said that the union had no choice but to accept Waldheim's offer.

Some U.N. officials close to Waldheim expressed doubts that staffers would give testimony, with or without immunity, because of their own vulnerability and because they still hope to be repaid.

One Waldheim aide said three staff members had admitted to him privately that they had loaned large sums to a man in a position to influence their promotions but insisted that the loans were unsolicited and were made on the basis of personal friendship.

Two other U.N. employes said that after the staff union had begun to look into the charges, the high official involved told those to whom he still owed money that he would repay them in a few months, when he leaves the U.N. At that time, he reportedly told them, he will get a $100,000 lump sum settlement from the U.N. to pay off the loans.