The leading rich nations of the world were urged yesterday by a senior international banking official to advance the International Monetary Fund at least $6 billion on a temporary basis to ease the IMF's cash shortage until next year, when its regular resources are to be augmented.

Without an emergency infusion of $6 to $8 billion, IMF officials fear that they may not be able to meet all legitimate borrowing demands from Third World nations.

Lamberto Dini, managing director of the Bank of Italy, and chairman of a rich nations' committee discussing this problem, said in a telephone interview from Rome that "in a situation like this, it is not reasonable for the IMF not to have the necessary reserves available."

He noted that "lending by the commercial banks to the less-developed countries has actually been negative" in the past few months, meaning that repayments have exceeded new loans.

Dini, chairman of the deputies of the Group of Ten rich industrial countries, said that he hoped his committee could act favorably on the emergency loan proposal in Paris on Sept. 15 and 16, in advance of the Group of Ten ministerial meeting in Washington on Sept. 24. The annual IMF/World Bank meetings will take place Sept. 27-30.

The Italian banker anticipates a preliminary discussion of his proposal among key central bankers at their meeting Sept. 12 in the Bank for International Settlements headquarters in Basle, Switzerland. European central banks, along with those of Japan and Canada, are being asked to advance at least $3 billion, with another $3 billion expected to come from Saudi Arabia.

In Basle and in Paris, officials also will discuss a reduction in the present "access" rights of borrowing countries, once IMF quotas are increased. Presently, a member nation can borrow up to 150 percent of its own quota, or deposits, in the IMF for three years--or 450 percent overall.

The question of whether the IMF for the first time should be allowed to supplement its resources by borrowing in the private financial markets will also be brought up at the G-10 deputies' session. West German Finance Minister Gerhard Stoltenberg has already said his country is firmly opposed to this idea. American officials have withheld comment, but are known to be more open-minded on the issue.

The Reagan administration is not so open-minded on the Dini rescue plan, believing that it cannot participate in the $6 billion emergency package as long as the fate of the $8.4 billion appropriation bill to increase U.S. support for the IMF and the General Agreements to Borrow is still in doubt before Congress.

But Dini suggested that there may be other ways for the United States to assume a share of what is meant to be a temporary burden, until the IMF gets full access to enlarged quotas (deposits by member countries) next year. Dini didn't specify it, but in the past, the United States has advanced money directly to countries like Brazil through the Treasury's Exchange Stabilization Fund, temporarily trading dollars for another nation's currency.

Meanwhile, IMF officials said that Managing Director Jacques de Larosiere was still seeking a consensus on the attitudes of member countries for the creation of a new issue of Special Drawing Rights, the IMF's international currency, for distribution to members.

On this issue, too, there seems to be a difference between German and American views. Stoltenberg has expressed opposition to a new SDR issue. But in a recent interview, Treasury Secretary Donald T. Regan showed more flexibility.

" . . . We were opposed to this at a time when we thought it might exacerbate worldwide inflation," Regan said. " But inflation is dying down . . . and if it can be demonstrated that it will help liquidity but not harm the world's monetary systems by inducing a lot more inflation, we would consider it." Regan added in any event that the United States would not support the huge SDR allocations sought by the poor nations, but only a modest issue.

Dini wants to set up the G-10 deputies meeting for Sept. 15-16 in Paris, because, co-incidentally, a meeting of the Organization for Economic Cooperation and Development's "Working Party 3" is already scheduled to take place on those dates, and there is a considerable overlapping of membership of the two groups. The U.S. representative for both, for example, is Treasury Undersecretary Beryl Sprinkel.

But it is a crowded week on the European financial calendar. For example, there is also a meeting of Common Market monetary officials scheduled for Brussels on Sept. 14.

American officials would just as soon put off all public talk of additional IMF resources until the annual meetings here, when it will be more or less inevitable. If the Dini group does not meet in Paris on Sept. 15-16, he said it will meet in Washington on Sept. 23.