The secretary of the Treasury could hardly been more charmingly hospitable -- or politically optimistic.

"I'd like to have you come over on the fifth of November and tell us what we really should do," purred G. William Miller to Alan Greenspan, a key economic adviser to GOP presidential hopeful Ronald Reagan.

"I'll be sleeping," the former chairman of Richard Nixon's Council of Economic Advisers replied laconically, deciding against a prolonged discussion of his post-Election-Day plans.

Greenspan passed on through a receiving line that included Federal Reserve Board chairman Paul Voicker and Deputy Treasury Secretary Robert Carswell at the National Gallery of Art's East Building last night, where Miller entertained 2,500 finance ministers, central bank governors and others representing 141 countries here for the 35th annual meeting of the International Monetary Fund (IMF) and World Bank.

Mostly, they were names and faces only somebody's banker might know. Many represented Third World countries eager for the IMF to liberalize its lending policies.

"Our problems are not of a cyclical nature like industralized nations', but more structural, needing longer repayment periods," said Bernard Coard, Granada's deputy prime minister and also its finance minister.

Ravaged by hurricanes and volcanic eruptions, small Caribbean countries such as Granada see as grim the prospects of being able to realize any financial returns from replanted coconut, citrus or nutmeg within traditional repayment periods when crop maturity takes anywhere from five to seven years.

Now with Burroughs Corp., Blumentahal dismissed talk of the collapse of the monetary system with "rumors of its demise are grossly premature . . . There are problems which contribute to it, some in this country, but they don't lead to any collapse.

And how, then, would he explain the number of best sellers on crisis investment?

"People like to be frightened for the same reason they go to horror movies," he said.

Elsewhere in the soaring gallery, Alan Greenspan was eating his dinner from a buffet of dwindling hors d'oeuvres.

"I oppose a bill that endeavors to put a gold standard in without first making the conditions that a gold standard function," he told a reporter inquiring about Sen. Jesse Helms' (R-N.C.) current efforts to enact such legislation. "I'm in favor of a gold standrad after we impose the degree of fiscal discipline that is required to make the dollar convertible into gold."

And no, said Ronald Reagan's man on Wall Street, he hoped he wouldn't have to move back to Washington even if his man in Middleburg does win.

"We've had some sympathy, but unfortunately the power structure of the IMF and World Bank is based on the financial support of these institutions," said Coard. "The richer countries have the critcal say in that decision-making, and as a result the concessions being made are not as rapid as necessary. We're fearful thatthe Third World countries -- the poorer ones and the ones in greater difficulty -- may collapse within the coming decade if structural adjustments aren't made by these institutions."

It was the theme that retiring World Bank president Robert S. McNamara has touched upon earlier in the day. In an emotional speech blaming OPEC nations for the current international economic crisis, McNamara voice broke done at one point, forcing him to pause to regain his self-control.

"You see," said one of the guests, "even a man who is like a robot can be emotional."

"All we can hope is that we get someone who will continue what he started -- expanding the resources of the bank and tickling the conscience of the developed world and rich countires," said Coard.

A couple of prospective successors were at the party, even if Mc(namara was not.

"I'm not in the running for anything," thundered Volcker to a reporter's observation that he was reportedly in the running. "I've got a job."

Equally adamant was former secretary of the Treasury W. Michael Blumenthal.

"Somebody said, 'Your name is in second place.' and I said I wouldn't ascribe too much importance to that Who the hell thinks up all this rubbish anyway?" Blumenthal asked a former Treasury Department aide.