The International Monetary Fund's executive board Thursday approved a EUR28 billion ($36.49 billion) loan for debt-beleaguered Greece despite fears by some members that political risks may derail the program.

The decision allows for an immediate disbursal of the first EUR1.65 billion tranche of the loan, though practically the payout may not be transferred to Athens until Monday.

As a small share of a joint program with the European Union, the loan helps Athens stave off default and the euro zone to temporarily prevent the debt contagion from spreading to other ailing countries in the region.

"We want to help prevent the contagion scenario," a person with direct knowledge of the board's deliberations said after the meeting.

Euro-zone countries Wednesday signed off on its lion-share portion of the joint EUR130 billion bailout package for Greece.

Still, several board members have expressed reservations about the ability of Greece to successfully carry out the four-year program. Brazil's representative to the IMF, Paulo Nogueira Batista, abstained from the decision, a diplomatic way of opposing the program, according to people familiar with the matter. Technically, there is no vote as the board decides based on consensus reached before the actual meeting. But the positions of each delegation are recorded in confidential minutes.

"There's very little room for slippage here -- it's a very tight timeline," a board member told Dow Jones Newswires after the meeting.

The IMF has repeatedly said the Greek program runs a very high risk of derailment given the depth of economic restructuring required for the joint IMF-European Union package. The IMF is especially wary given Greece's track record of failing to meet many of its fundamental program targets.

IMF staff reported to the board some small but encouraging signs that the program could be more politically feasible than originally thought, citing polls that show a strong majority of Greeks want to stay in the euro zone and data indicating Greeks hold a significant amount of non-Greek assets outside the country that could be used to help spur the economy back to health.

Fund staff have warned that a failure of Athens to implement needed economic changes would push financing costs up to EUR245 billion. That's compared to combined debt-restructuring costs and official-sector lending under the new program of around EUR230 billion.

According to the person with direct knowledge of the board's deliberations Thursday, the board is split over whether the fund should provide anymore cash to cover any possible future financing gaps.

"Many board members are not prepared to give anymore money," the person said.

Europeans sitting on the board want the fund to leave open the possibility, but many others don't think the IMF should increase its exposure to Greece, given both the amounts the IMF has lent to Athens and the risk of default.

"The debt trajectory is extremely sensitive to program delays, suggesting that the program could be accident prone, and calling into question sustainability," IMF staff wrote in a recent report to the IMF board. IMF staff assume in that report that additional financing requirements would be covered under the terms of the European Financial Stability Fund, the euro zone's bailout facility.

"It may take much more time than assumed to identify and implement the necessary structural reforms to improve the primary balance," IMF staff warned in the report. "And concerning asset sales, delays may arise due to market-related constraints, encumbrances on assets or political hurdles," they said.

The fund is attempting to counter what many board members fear is over-exposure to Greece. Compared to its European partners' contributions, the IMF's EUR28 billion loan is proportionally smaller than the bailout package it succeeds. The IMF and Europe abandoned the first program after it failed to stem the crisis, replacing it with tougher economic conditions, a restructuring of EUR206 billion in privately held Greek government bonds and more bailout cash. The fund had already issued more than EUR20 billion in credit to Greece under the previous program, but cancelled the remaining EUR10 billion in disbursements in favor of the new package.

Also, the IMF is extending its payout period by a year, making it a four-year program instead of three. The longer payment schedule allows for smaller disbursements and preserves more IMF capital should the IMF halt payments for program failure.

Some economists still predict Greece ultimately may have to pull out of the euro zone or, at the very least, restructure its debt again. Many have said Greece already is at the limits of its ability to enforce already-approved policies.

Several of the most powerful politicians in the Greek government have given the IMF written political commitments to carry out the economic reforms. Some, however, expect that commitment to the program may wane after elections planned in the coming weeks.

Some analysts say the fund is using the loan program for Greece to buy time for other ailing euro-zone countries to put their economies back on a healthy path and for banks to insulate themselves against a worsening of the debt crisis. The fund is urging euro-zone leaders to boost the size of its general bailout fund by at least half and to use some of that cash to bulk up banks' capital defenses.

-By Ian Talley, Dow Jones Newswires; 202-862-9285; ian.talley@dowjones.com

--Costas Paris in London, Matina Stevis in Brussels, and Sudeep Reddy of the Wall Street Journal in Washington, D.C., contributed to this article.