THURSDAY, JULY Cl  
When President Nixon determined in early February 1973 that the U.S. dollar had to be devalued for the second time in 14 months, he sent his under secretary of Treasury, Paul A. Volcker, on a secret mission to Tokyo and Bonn to get the agreement of the nationÛªs two most important trading partners.</br></br>Volcker, who had played a key role since 1969 in patching up a series of gold and dollar crises, tucked his 6 foot 7 frame and everpresent cigar into an Air Force plane and headed for Tokyo.</br></br>There, he left a hat with his name at the Ministry of Finance, but the thoughtful Japanese got it back to him in time. In Bonn, however, his gangling frame almost blew the cover when a German reporter spotted him.</br></br>But with the dollar deal in his pocket, he telephoned the details to Treasury Secretary George Shultz. Nixon announced it Feb. 12, 1973, and a new era of fluctuating exchange rates was formally launched.</br></br>But the hopes of Volcker and others then that the leading nations of the world could work themselves back to a greater sense of monetary stability havenÛªt been fulfilled, primarily because of the upheaval caused by oil price increases and worldwide inflation.