Third World debt grew at a smaller pace last year, but still reached nearly $900 billion, and is expected to near the $1 trillion level by the end of this year, the World Bank said yesterday.

In a cautiously optimistic assessment accompanying a new edition of the World Debt Tables, Vice President and Chief Economist Anne O. Kreuger said that the "financial phase" of the debt crisis, in which nations could not service their debts, "is now largely over."

She said the borrowing countries for the most part are "well into" the second phase of "correction" before the final and essential phase of sustainable growth.

Third World debtor nations fall into three groups, according to the bank -- those that have avoided serious debt crisis problems, such as South Korea and India; those now "largely out of the woods," such as Mexico; and those further behind, with growth at least a year or two away -- or longer, as in sub-Saharan Africa.

Bank officials, in response to questions, said that Brazil and Argentina, still negotiating with the IMF, "are somewhere in between the first two groups."

Kreuger said that favorable developments last year were a vindication of the "case-by-case" approach adopted by national lenders and international institutions. She acknowledged the "very tough" belt-tightening measures put in place by the borrowers, and had a special word of praise for the International Monetary Fund's management of the problem.

On the other hand, the bank's economist cautioned that extension of the hopeful scenario depends on the ability of borrowers to expand their export earnings. In turn, this depends heavily on the ability and willingness of the richer nations to sustain a 3 percent real growth rate, lower interest rates, and to "roll back" protectionist measures that restrict exports from the Third World.

"I am optimistic. If the industrialized countries can achieve that 3 percent -- or even 3.5 percent -- growth and if they can maintain open trade policies, permitting access to their markets by the developing countries, then the outlook is good," she said.

If the advanced countries should try to place a ceiling on imports from the less developed countries (LDCs), "instead of the painful unwinding" now foreseen, the debt crisis could not be resolved, Kreuger told a press conference.

The precise total of long- and short-term LDC debt of 104 reporting countries was up 6 percent from $843 billion in 1983 to $895 billion last year, and is projected to reach $970 billion by the end of 1985. These figures are partially estimated; complete country-by-country tallies do not go beyond 1983.

Nicholas Hope, chief of the bank's external debt division, noted that "the weakness of the debt tables is that they don't show assets. For example, where Mexico's and Brazil's gross debt increased, their net debt declined."

Overall, the real economic growth rate in the Third World jumped substantially in 1984 to 4.1 percent from 2.3 percent in 1983, allowing what the bank said was the first significant overall gain in per capita incomes in these nations. The bank's forecast for 1985 is 4.5 percent.

The biggest improvements were registered by major debtor countries, such as Mexico, the tables show. Their current account deficits fell sharply, and in some cases, debt negotiations opened the way for multiyear reschedulings, notably the $49 billion restructuring of Mexico's debt that the bank called a model for the future.

On the other hand, the bank noted that the 12 largest debtor countries had "negative net transfers" of $15 billion in 1984, compared with $10.1 billion in 1983, meaning that they had paid that much more to service their debts than money they received from new loans.

The concept of net transfers is considered significant. Other things being equal, as the report published yesterday says, "in a given year, a country would be better off with positive rather than zero or negative net resource inflows."

The concern over negative net transfers is heightened in the present situation because "the direction of the flow was reversed in 1982 when the borrowers' income levels were still relatively low, and because the abruptness of the reversal made this phenomenon very difficult to handle," the report says

Hope offered the opinion, nonetheless, that confidence in the Third World countries is growing