Top presidential aide Hamilton-Jordan has been given an unannounced assignment of the utmost difficulty and political sensitivity: to make sure President Carter gets the two-thirds Senate vote needed to ratify a new Panama Canal treaty.

That means Carter is turning to his most trusted lieutenant, architect of his presidential nomination, for what promises to be one of the most heated treaty-ratification fights in Senate history, Jordan, who gets bored with philosophic consideration of issues, tells friends he is delighted with the prospects of a knockdown fight for votes, reminiscent of the presidential campaign.

Selling the canal treaty is only one of several new responsibilities for Jordan that underline his primacy on the White House staff. He also oversees relations with the American jewish community, supervised negotiations with Congress on the water projects and will have responsibility for handling Senate ratification of any arms-limitation treaty signed with the Soviet Union.

In privately claiming there are only 30 hard-core Senate votes against the canal treaty, Jordan may be underestimating his task. During a recent chat with the President, Sen. Jesse Helms (R-N.C.) counted 43 opposition votes (nine more than needed). Other foes of the treaty believe the total may climb over 50 once a major media blitz begins playing on deep-seated public apprehension.

Footnote: Assignment of White House aide Joe Aragon as Jordan's deputy on the canal treaty betrays some dubious political thinking. Aragon, formerly head of the Democratic National Committee's Latin America division, is supposed to line up Spanish-speaking Americans for the treaty.

A bizarre alliance of corporate big business and liberal White House aides is burying one of President Carter's campaign promises on tax reform: ending double taxation of corporate profits and stockholder dividends.

This coalition's success is made all but certain by the fact Budget Director Bert Lance has just joined it. Presidential confidant Lance's reason for opposition: the $14 billion to $18 billion revenue loss.

Business opposition, led by the influential Business Roundtable, results from fear that a stockholders' tax credit to offset taxes paid at the corporate level will squeeze corporations for higher dividends. Liberal aides in the White House, led by policy chief Stuart Eizenstat, see the proposal as making that he favors rich stockholders over blue-collar wage-earners.

Despite official denials, Director Paul Warnke's quiet purge of hard-liners at the Arms Control and Disarmament Agency (ACDA) continues with a new assistant director bound to raise eyebrows at the Pentagon: Adam Yarmolinsky, now a University of Massachusetts professor.

Yarmolinsky infuriated the military as a Defense Department civilian aide in the 1960s, and his selection shows how much Washington has changed over a decade. In 1966, President Johnson dumped him as deputy director of the poverty program when right-wing Southern congressionmen complained Yarmolinsky was too far to the left. In 1977, his appointment by President Carter to an incomparably more sensitive post at ACDA should win easy Senate confirmation.