Treasury Secretary James A. Baker III's proposal to encourage a new cash flow to Third World debtor nations is "fuzzy and unfocused" and is likely to fail unless strengthened, Rep. Stan. Lundine (D-N.Y.), chairman of a House subcommittee on international finance, said yesterday.

Lundine emphasized that he endorsed the Baker initiative, which calls for reforms in the economies of the borrowing countries, a $20 billion increase in commercial bank lending and a doubling to $9 billion of multilateral agency loans to the Third World over three years.

"But the Baker plan is not really a plan, and there is not enough money in it," he said. He warned that unless Congress is able to force action to resolve the international debt crisis, there could be a collapse of major U.S. banks that have made huge loans to borrowing countries.

"If we do nothing, there is a very high risk that some of these nations will be unable to pay their debt. It is already clear that some are unable even to pay the interest," Lundine said. "We all know it's a ticking bomb, and we haven't been willing to face up to it."

Lundine was highly critical of the World Bank, which he labeled "a very bureaucratic institution" that had failed to disburse money quickly enough to needy countries, and said he would propose legislation beefing up the bank's role.

He also wants the Treasury to explore "more flexible write-off arrangements" for banks with a heavy exposure in Third World countries in exchange for their willingness to continue to make loans.

This and other proposals relating to the debt crisis will be incorporated into an omnibus bill on trade legislation being formulated by the House Democrats. Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said the bill should reach the floor in May. Lundine believes it urgent to focus on the link between the debt crisis and the huge national trade deficit, about one-third of which is ascribed to the loss of markets in Third World economies.

In return for increased monetary aid, he would require Third World nations to abandon some of their protectionist devices. Lundine said such trade liberalization could revive U.S. exports to those countries and help dampen protectionist sentiment here.

The most significant of Lundine's legislative plans for the World Bank would be an increase in its so-called "gearing ratio" from 1:1 -- which limits lending authority to the exact amount of the bank's capital -- to a 2:1 ratio, which would allow the bank to double its lending power with the same capital.

Lundine conceded that the proposal is a controversial one that frequently has been considered by the bank in the past and always abandoned in the fear that it would jeopardize the AAA rating of World Bank bonds, achieved in part because of the highly conservative 1:1 gearing ratio. Commercial banks typically lend 20 or 30 times their capital.

Lundine said that Congress would prefer a boost in the gearing ratio rather than an increase in the bank's capital, which would require larger budgetary outlays at a time of constraint under the Gramm-Rudman-Hollings process.

But a spokesman for the bank said that the institution remains "dead set against changing the gearing ratio" and is proceeding with a plan for detailed discussions of a general capital increase at the meeting of the International Monetary Fund/Bank Development Committee on April 10-11.

Lundine said that his legislation also would direct the Treasury to report to Congress by this fall on whether a general capital increase will be needed by the bank in 1988. Both a change in the gearing ratio and a capital increase might be needed, he added.

The Reagan administration should come forward with any request for a general capital increase at the same time it asks for new funds for the International Development Agency, the World Bank's concessional aid arm, he said. "I would rather go in with everything at one time, instead of parceling it out," Lundine said.