The issue of debt sustainability has long pitted the I.M.F. against Greece’s other creditors. Germany, Europe’s austerity enforcer, has clashed with the fund, and the I.M.F. has refused to offer financial backing in the third bailout, a symbolic step, though one that analysts had been keenly watching for. Berlin is loath to offer additional debt relief to Athens, whereas the I.M.F. has said it does not believe Greece’s debt can be repaid without creditors easing up.

It hit the point home again on Tuesday. The fund said that despite recent debt relief efforts, which include extending the payback time for Greece’s bailout loans, reducing the country’s debt “can only be sustained over the long run under what appear to be very ambitious assumptions about G.D.P. growth and Greece’s ability to run large primary fiscal surpluses, suggesting that it could be difficult to sustain market access over the longer run without further debt relief.”

Though Greece’s economy is growing, it is still only three-quarters of its precrisis size. Gross domestic product has expanded since the middle of last year, buoyed by an apparent renewal in exports. But much of the export growth comes from refining imported oil and exporting the final product — an activity that sustains tens of thousands of jobs, but does not filter through to the broader economy.

Unemployment, which has fallen from a peak of 28 percent, is still stuck above 20 percent, the highest in the eurozone. Over half a million Greeks left during the crisis in a brain drain that has hampered a recovery. Worryingly, poverty has “risen dramatically,” according to the Organization for Economic Cooperation and Development, a group of rich nations.

The social situation has deteriorated so markedly that the I.M.F., which many Greeks blame for worsening their plight as one of the original enforcers of harsh austerity, repeated its call for the Greek government to proceed with planned increases in targeted social support and investment spending. It also suggested reducing tax rates that in some cases reach as high as 70 percent of a person’s income. The Greek government jacked rates up so sharply in the last couple of years that the country’s notorious black market has grown again.

Even as it proposed pulling back on some of the harshest austerity, though, the fund recommended maintaining elements that have created hardship for large numbers of average Greeks.

Among other things, it urged the government to stick with a plan to cut pensions further next year, and to resist restoring collective bargaining agreements, which cut the iron power of unions but also led to a drop in wages. Allowing the return of such deals would reverse a nascent recovery in employment and competitiveness, the fund said.

“Greece has reached this point thanks to enormous efforts,” the fund added. “Greece should now consolidate and extend its success by addressing, with determination, its remaining challenges.”