As federal regulators prepare to loosen or eliminate the rules that have restricted the largest broadcasters from growing bigger and owning newspapers, senior executives from Viacom and the Tribune Company asked the Senate today to let regulators proceed without intervention.

The executives, Mel Karmazin of Viacom and Jack Fuller of Tribune, said the concentration limits were anachronistic and had contributed to new and intolerable business hardships.

"The broadcast business is dramatically changing all around us," Mr. Karmazin testified before the Senate Commerce Committee. "Our audiences are dwindling, our margins are contracting and our share of advertising revenues is declining. The impact on consumers, who should be central to this debate, do not benefit from the status quo when it is irrational, anticompetitive and an obstacle to expanded choice."

But Senator Ernest F. Hollings of South Carolina, the new Democratic chairman of the Commerce Committee, said that the rules had already been relaxed too much and that what remained of them was central to preserving local programming and a diverse array of voices on the airwaves.

Mr. Hollings chided Mr. Karmazin for portraying an industry in gloom and doom. After reeling off a series of figures that showed Viacom under Mr. Karmazin and its chairman, Sumner M. Redstone, had remained highly profitable...