The Third World debt problem is now manageable, and will improve significantly over the next few years as the global economy recovers, according to a new study of 19 of the largest debtor countries.

In the study, economist William R. Cline, like International Monetary Fund Managing Director Jacques de Larosiere, says that the problem of Third World debt "is one of temporary illiquidity, not fundamental insolvency."

Nevertheless, he adds that the debt crisis "seems likely to continue to threaten the world economy and international financial stability for at least the next few years."

The report, issued yesterday, urges quick adoption of larger quotas for the IMF, and also recommends that the World Bank and other multilateral development banks try to accelerate loans.

Cline concludes that sweeping proposals for reform that would consolidate Third World debt into longer-term, lower-interest loans--such as those made by Peter B. Kenen of Princeton University, Rep. Charles E. Schumer (D-N.Y.), Sen. Bill Bradley (D-N.J.), and New York banker Felix Rohatyn--not only are unnecessary, but "constitute a panic-based action that would tend to turn good debt into bad debt."

His report was sponsored by the Institute for International Economics, a research group in Washington funded by the German Marshall Plan of America.

In additional highly critical references to various debt reform proposals, the report says that most of them have misdiagnosed the debt situation, and several "of the schemes would tend to choke off new bank lending to LDCs," or less developed countries. Referring specifically to a proposal by Kenen (who also happens to be on the institute's advisory committee), Cline said:

" . . . The choking off of new loans would precipitate precisely the crisis that the authors of such proposals fear.

"Most of the reform proposals would make sense only in an environment in which no new loans whatsoever are expected, but maturities are being lengthened; they do not address the need for new lending."

Cline's alternative prescription, which is based on expectations of real economic growth in the industrial world of between 2 1/2 and 3 percent over the next three years, is to set up some form of emergency contingency planning based on negotiating debt problems on a case-by-case basis. The analysis and recommendations in many ways parallel the policy already set out by the IMF.

Updating material he had made public before, Cline also reported that the loans of the nine largest American banks to Third World borrowers now amount to almost 300 percent of their capital. He supported the Federal Reserve's proposals for increased regulation of foreign lending.

He said that, among additional steps that might be considered to save the financial system from a major disruption would be for the debtor countries to impose sanctions "on banks which jeopardize the system by trying to pull back their existing loans or refusing to increase their exposure in an internationally coordinated rescue program."

Cline predicts that the debtor countries of the developing world and Eastern Europe will continue to run current account (trade and service) deficits of about $75 billion a year through 1986.

He concedes that the red ink would flow in even greater volume and be "virtually impossible to accommodate without further major strain on the international financial system" if the 2 1/2 to 3 percent growth rate in the First World is not achieved.

The improvement that Cline foresees--which he reports already has begun in some major nations, such as Mexico and Argentina--will go forward as Third World nations resume the growth in their export markets. But Cline warns that the apple cart could be upset if there are "any significant new increases in interest rates and protectionist trade barriers."