Looking to the mounting bill for the drugs that keep millions of poor people alive, they also said China and other fast-advancing economies could shoulder more of their own burdens in the future, freeing up resources for countries mired in poverty.
Speaking on the sidelines of the International AIDS Conference, Global Fund chief Michel Kazatchkine and UNAIDS head Peter Piot said they believed countries still stood by the fast-approaching 2010 target, although they doubted the goal would be reached by all.
"When we look at global targets, none of us believes that it will be 100 percent everywhere," Kazatchkine told a group of reporters.
"But if you look at individual countries, and if you look at the percent that have achieved universal coverage or (will) be close to universal coverage, there may be much more than you may think of."
The 2010 target, enshrined in a June 2006 UN General Assembly resolution and supported by the Group of Eight (G8), is emerging as a touchy political issue.
Three million badly-infected poor people now have been able to grasp the drug lifeline, thanks to a big scaleup in the last two years, but this is still two-thirds short of the total in need and time is running out to meet the deadline.
As a result, activists have closely scrutinized the July G8 summit statement, and last week's UNAIDS report on the state of the pandemic.
Some see a weakening verbal commitment to 2010 and a dangerous slippage to 2015, which is also the end-date for the UN's Millennium Development Goal on reversing the spread of HIV.
Piot, UNAIDS' executive director, said, though, "the (2010) commitment has not changed whatsoever.
"2010 is 18 months from now," he admitted. "What we've seen is that in a number of countries, they've already reached their universal access targets, others not."
Some countries could achieve universal access in 2011 or 2012, in line with their national programs, Piot's spokesman explained.
In other comments, both Piot and Kazatchkine, who is executive director of the Global Fund to Fight AIDS, Tuberculosis and Malaria, said there would have to be fresh ideas for tackling the mounting cost of keeping people alive with antiretroviral drugs.
Some 33 million people around the world are infected with HIV, 90 percent of whom live in developing countries.
By some estimates, universal access will cost 54 billion dollars per year in 2015 -- and the bill will endure for decades, as the treatment is for the rest of one's life.
Kazatchkine said he looked to the G8 countries, which account for 90 percent of contributions to the Global Fund, to meet their commitments.
So far, they are only a little more than a third to the way of fulfilling the pledges they made at their 2005 Gleneagles summit.
He and Piot also said that middle-income countries that were advancing rapidly towards prosperity should, in future, shoulder more of the bill.
"If you are in the lower tranche of middle-income countries, you would contribute let's say 30 percent and the Global Fund would contribute 70 percent.
"If you are in the upper tranche of middle-income countries, the Global Fund would contribute 30 percent and you would contribute 70 percent," said Kazatchkine.
He noted that Russia, buoyed by the influx of petrodollars, has pledged to reimburse 300 million dollars received from the Global Fund.
"I think this opens the door to China and one day maybe India, but at least (to) those countries that are generating so much wealth," he said.
Kazatchine also said he was approaching oil-rich countries in the Middle East for help. He said he had been received sympathetically, although "it takes time before you actually bring those people to the table."
"China can perfectly pay the treatment of every single Chinese who need it with HIV, Mexico can do it," Piot said.
"It's a matter of political choices in terms of allocation of resources. If these countries do that, then the money from the Global Fund and international donors can concentrate on the poorest countries."
But, he cautioned, "That will require some very heavy lifting, politically."