Rebellious bondholders at Kay Jewelers Inc. won a major victory yesterday when the British jewelry firm that wants to buy Kay sweetened its offer for the bonds from 75 cents to 90 cents on the dollar.

The offer by Ratners Group PLC of London appeared to put the proposed $350 million takeover back on track after doubt about whether Ratners could persuade Kay bondholders to sell for 75 cents. Ratners had said it would not acquire Kay unless it could buy more than half of each of two Kay bond issues.

As of late yesterday, Ratners said it had bought almost 75 percent of 12.785 percent bonds at the higher price but only 10 percent of the 12.5 percent issue.

Ratners's recent attempt to buy the bonds for 75 cents on the dollar was met with near-solid opposition by institutional investors, who hold most of the Kay bonds.

One of the leaders of the unhappy flock was Deborah Pederson, high-yield bond analyst for IDS Financial Services, who finally agreed to sell her bonds after weeks of negotiations with Ratners. Pederson said, "It might have been more noble to hold out for par {$1} but it would not have been in the best interests of the shareholders."

Charles T. Akre, head of Akre Capital Management in Alexandria, called the 90-cent offer "very reasonable for bondholders."

The bondholders, who paid $1 for the bonds, had earlier said they were unhappy because Ratners was asking them to take a 25-cent "haircut" while offering common stockholders a "significant" premium for their stock.

Ratners officials said the original offer was fair because the bonds had been trading for 45 to 50 cents on the dollar. Once the investors made it clear to Ratners that they would not accept the 75-cent offer, Ratners and the bondholders began to negotiate.