Nassau Broadcasting Corp. is auctioning 30 of its New England radio stations after obtaining court approval to sell some of its more valuable stations earlier this month, Dow Jones DBR Small Cap reported yesterday. The auction began on May 3 but was adjourned until yesterday, according to court papers filed. The highest offer received for the 30 stations so far is a $14 million credit bid submitted by the agent for the company's senior lenders, an affiliate of Goldman Sachs Group Inc., which recently obtained court approval to buy 11 of the company's stations.