Last fall, Treasury Secretary James A. Baker III electrified an international audience in Seoul by offering a new initiative on Third World debt that promised a break with the Reagan administration's ideological past.

Baker, recognizing that the heavily indebted borrowers needed relief, proposed that some 15 nations receive an additional $20 billion in loans from commercial banks over the next three years, provided that the borrowing countries introduced economic reforms along free-market lines -- including a welcome mat for foreign investment.

At the same time, he called for a doubling of loans from the World Bank and the Inter-American Development Bank to a total of $9 billion.

But it has been downhill from there: The follow-through, after the original excitement faded away, has been disappointing. No banks have stepped forward to lend more money, and the World Bank and IADB are light-years away from meeting Baker's target.

Worst of all, even though the World Bank was expected to play a central coordinating role in activating the Baker plan, the Treasury team never came up with its own candidate to succeed bank President A. W. Clausen, who leaves his post at mid-year.

Thus, the administration has been flailing around almost aimlessly trying to fill this key post. For a while, after considering several New York bankers, the administration thought of moving William E. Brock from his post as secretary of Labor into the bank. Privately, Secretary of State George P. Shultz -- who has been actively involved in this process -- urged Brock to take the job.

Brock's main credentials for the bank presidency lie in his high standing in the international financial community, which remembers his outstanding record as United States trade representative.

But Brock's wife recently passed away, and Brock sensibly put first things first: The need to spend time with his children -- time, he told me in an interview, that wouldn't be available if he threw himself into the task of getting up to speed on debt and development issues.

Brock having taken himself out of the running, new life may have been breathed into the self-promoted candidacy of J. William Middendorf, U.S. ambassador to the Common Market and a former secretary of the Navy under President Nixon. Middendorf, who talked to President Reagan last week, has openly lobbied for the job, even though some major nations make no secret of their belief that he has few qualifications to run the World Bank. Said one European privately: "I've got my fingers crossed; Middendorf would be a disaster."

Middendorf is identified with Republican right wing causes, including a return to the gold standard. Bruce Bartlett of the Heritage Foundation, who is well clued into Reagan administration thinking, suggests that Middendorf has the backing of White House Chief of Staff Donald T. Regan, who has voiced his "disdain" for the bankers who make up the balance of the short list of possibilities. "Hence, one would have to conclude that Middendorf will, in all likelihood, be the next president of the World Bank," Bartlett says.

Meanwhile, the Third World debtors, having suffered austerity pains under the IMF's loan programming in the past four years, haven't rushed to change the way they manage their economies. And despite the well-orchestrated lip-service paid by commercial banks to the wisdom of the Baker debt initiative, no way has been established for them to make loans conditioned on the adoption of the market-oriended policies Baker called for.

At the same time that observers question whether the Baker debt plan ever will be more than a good idea that didn't jell, questions remain about another of his "pragmatic" initiatives, the reinvigoration of the Group of Five process last Sept. 22.

On that date, Baker convened a New York meeting of the major monetary nations -- the United States, West Germany, Japan, France and Britain -- at which they promised to take coordinated economic policy actions, starting with a downward push on the dollar. The G-5 did, in fact, depress the dollar substantially, and that should help reduce -- but not solve -- the problem of enormous American trade deficits.

But the willingness of the Reagan administration to intervene in exchange markets -- abandoning what the Europeans like to call "benign neglect" -- still leaves open the question of whether there can be agreement on a new era of exchange-rate management.

The rest of what the Group of Five promised to do to expand economic activity around the globe has borne little fruit: Japan and West Germany still refuse to use fiscal measures to boost their economies, and Germany, until last Thursday, had resisted cutting interest rates.

In the interim, Reagan and the G-5 partners have had two lucky breaks: the decline in global interest rates and -- thanks to the Organization of Petroleum Exporting Countries -- the collapse in oil prices, in effect a tax cut that will help accelerate growth everywhere except the unfortunate oil-producing countries. But to take real advantage of the moment, West Germany, Japan and the United States will have to deliver fully on their Sept. 22 commitments.

On monetary reform, the U.S. has to settle an internal debate over whether it wants to change the floating rate system. It would appear that Baker is pushing for change, while Shultz is a hold-out.

Speeded-up action is needed on the Third World debt front. Mexico is in desperate trouble, and may be near the end of its rope. A successor to Clausen must be found, and he or she must have an outstanding international reputation -- comparable to Brock's.

And as Rep. Stan Lundine (D-N.Y.) implies, the additional Third World aid proposed by Baker must be doubled or tripled -- and paid out. Lundine, chairman of a House subcommittee overseeing some of these problems, speaks of the debt as "a ticking bomb, and we haven't been willing to face up to it."

In a way, I think there may be an analogy here with the ill-fated space shuttle Challenger. The signals of potential disaster have been flashing persistently, and persistently ignored. It took the loss of the shuttle, the mission and seven lives to trigger a harder look at the whole program. We shouldn't wait until an international crash -- say, a Mexican moratorium that sends a few big American banks into bankruptcy -- shakes us out of the present lethargy.