The choice of Agriculture Secretary Clayton K. Yeutter to head the Republican National Committee marks the retreat of the RNC from prominence. Yeutter is well-liked and an effective fund-raiser. But, asks GOP consultant Eddie Mahe Jr., "What does he bring to the job?" Yeutter has neither the political genius of the ailing Lee Atwater nor the ideological flair of former drug czar William J. Bennett, who turned down the party post for financial reasons. The RNC is now likely to take a backseat to President Bush's soon-to-be-formed reelection committee. Meanwhile, the White House is likely to put a failed Senate candidate in the Agriculture post. Leading contenders are former Representative Thomas J. Tauke of Iowa and former Senator Rudy Boschwitz of Minnesota.