In one administration after another, the position of Commerce secretary has been filled by a close friend of the president who serves as a combination of political counselor, front man and congressional arm-twister -- without exercising much obvious power over policy. Donald L. Evans, who resigned the job yesterday, was a classic example.

Evans's most important function, according to administration insiders and outsiders, was as a confidant and extension of President Bush -- advising the president on tax cuts, cajoling Republican lawmakers to approve legislation lowering trade barriers and selling the administration's policies with key groups.

"He was a fairly good advocate of trade liberalization. He made some fairly constructive statements with regard to the U.S.-China relationship. But it was an exercise in treading commercial water," said David J. Rothkopf, who was deputy undersecretary of commerce in the Clinton administration. "Almost undoubtedly Evans's greatest legacy is an invisible legacy -- the legacy of best friend of the president."

Evans, 58, who plans to return to Texas in January, is likely to be replaced by Mercer Reynolds III, a Cincinnati businessman who was finance chairman of the Bush-Cheney campaign, according to administration officials. Reynolds helped Bush buy into the Texas Rangers baseball team and was ambassador to Switzerland earlier in the administration.

Evans said in a letter to Bush that he has "concluded with deep regret that it is time for me to return home."

Bush called Evans "one of my most trusted friends and advisers."

A fellow Texas oilman who helped Bush in his first congressional race in 1978, Evans helped orchestrate the tax cuts that Bush pushed through Congress in his first term, even though the Treasury Department holds primary responsibility for tax policy.

As a man known on Capitol Hill to have the president's ear, he helped shepherd legislation giving Bush power to cut trade deals with other nations, even though the administration's point man on that issue has been U.S. Trade Representative Robert B. Zoellick. On one major issue -- the tariffs that the White House imposed on imported steel in 2002 -- Evans exercised influence because of his close ties to the industries that were affected. According to administration officials, he urged Bush to lift the tariffs in 2003, citing their adverse impact on steel-using firms. The president did so, although many other factors played a part in that decision.

Staff writer Mike Allen contributed to this report.