The International Monetary Fund is near an agreement with Saudi Arabia under which the wealthy oil-exporting nation will lend the IMF over $4 billion a year for the next two years, with the possibility of extending the deal for a third year.

In exchange, the Saudis are seeking a doubling of their voting power in the IMF which would give them the sixth-highest rank in the 130-member lending agency, behind only the United States, Great Britian, West Germany, France and Japan.

The money that the Saudis would put up -- technically, the equivalent of 3 billion to 4 billion special drawing rights (SDRs) each worth $1.22 -- proably would be supplemented by an additional 1 billion SDRs from Kuwait and the United Arab Emirates. That would provide a total of between 4 billion and 5 billion SDRs, or about $6 billion a year, which the IMF desperately needs for lending to hard-pressed poor countries.

At the moment, the IMF has available to it usable hard currencies amounting to only about 20 billion SDRs. Thus, an infusion of another 5 billion SDRs this year would boost the total by fully 25 percent. The Arab nations contributions, if they become available quickly, would repalce the so-called "Witteveen Facility," which is expected to run out in a few weeks. The Witteveen facility, named after former managing director H. J. Witteveen, was a special $10 billion fund collected to help needy countries surmount balance-of-payments difficulties.

The deal with the Arabs which IMF Managing Director Jaques de Larosiere has been pursuing for well over a year, presemably would be ratified by the IMFs Interim Committee at its May meeting in Libreville, Gabon. At this point, it appears that the Saudis, entirely willing to turn over hard cash to the IMF, are pressing the agency to make a decision. "They say, 'Let's go ahead and get something done,'" an IMF source says.

According to well-informed sources, the Saudis feel that if they attain greater voting power in the IMF through enlarging their quota -- that is, their deposits -- in the agency, they will be able to fight more effectively to gain the Palestine Liberation Organization observer status for IMF annual meetings.

Presently, Saudi Arabia is entitled to its own seat on the board of executive directors because it is one of the largest lenders to the organization. But according to IMF officials, the Arab nation feels "it will have a better leg to stand on in the internal debates" if it became, in effect, one of the "Big Six" powers ranked according to quotas in the Fund.

For the last two years, the PLO has sought observer status at the annual joint meeting of the IMF and World Bank and has been rebuffed by the existing power structure of the two organizations, especially by the United States. At the 1980 annual meeting in Washington, the PLO was kept out, after a bitter fight, only by eliminating all observers from the sessions. o

The Reagan administration, even more firmly than the Carter administration, is dedicated to keeping the PLO our of IMF-World Bank activities. A high administration official said in an interview that he is adamant against PLO admission and is prepared to say to the two organizatons: We have no opposition to the PLO so long as you don't discriminate -- you must be prepared to admit every terrorist organization in the world."

Nonetheless, other Reagan administration officials recognize that the Saudis are playing a "role of moderation in the Middle East" and are unlikely to oppose an IMF-Saudi deal in which the quid quo for a big Saudi is an enhanced role for the Saudis in the IMF.

But there remain a lot of details to be worked out. The Saudis, whose quota presently amounts to 1.74 percent of the total (providing 1.69 percent of the weighted votes) would like to have 3.5 percent. That creates something of a sensitive issue, because it would slid the Saudis in the power structure just ahead of Canada (3.4 percent) and Italy (3.1 percent). Moreover, the extra voting power assigned the Saudis would require fractional downward adjustments for everyone else in the IMF.

American officials have not taken a specific position yet on the Saudi quota but probably would be sympathetic to Canadian and Italian efforts to maintain their currently prestigious rankings. A Saudi quota just over 3 percent -- if they would accept it -- would rank them eighth, behind Canada and Italy.