The finance ministers and central bankers of the world's five leading industrial nations will hold a special meeting in New York today amid signs the Reagan administration may be prepared to take stronger actions to push the dollar lower in international currency markets to deflect mounting protectionist trade pressures in Congress.

Treasury Secretary James A. Baker III and Federal Reserve Chairman Paul A. Volcker are scheduled to meet for five hours at New York's Plaza Hotel with their opposite numbers from Japan, West Germany, Britain and France.

The meeting of this so-called "Group of Five" will take place less than 24 hours before President Reagan is expected to outline the administration's refurbished trade policy in a White House speech to a group of U.S. businessmen.

Sources here and in Europe speculated that a main topic at the New York meeting will be the need to increase the value of the Japanese and European currencies against the dollar, at a time when underlying trends in the major economies are coming closer together. Strengthening the value of the other currencies, in effect, would reduce the value of the dollar, make U.S. goods more competitive abroad and -- eventual- ly -- ease the current U.S. trade deficit.

If the United States indicates a willingness to push for appreciation of Japanese and European currencies, it would be a significant change in administration policy. As such, it would provide a key financial link with Reagan's recent commitment to a more aggressive trade policy.

The problems of Third World debt, and the need to maintain satisfactory growth rates without renewal of inflation, also are expected to be discussed as a prelude to the annual meetings of the World Bank and International Monetary Fund in Seoul next month. The Group of Five frequently meets just before annual meetings of the IMF and World Bank. But word of today's meeting came unexpectedly in a terse, one-paragraph statement from the Treasury Department. Treasury officials would give no further details, but it was learned that they had been holding bilateral meetings since the end of June in preparation for a G-5 session.

On the other hand, officials of one of the other four countries said that definitive notice of the meeting was given to them only on Friday.

In his discussion of the trade problem at the White House Monday, the president is expected to indicate that he will back legislation strengthening U.S. responses to unfair and illegal trade barriers among several U.S. trading partners.

But the understanding that may be reached today with the four other major nations on exchange-rate relationships would indicate that the administration also is willing to move more aggressively to get a better alignment of other currencies with the dollar. Its position until now has been not to intervene in exchange markets except when it considers conditions "disorderly."

In the intervention process, a central bank buys its own currency in foreign exchange markets when it is going down, or sells it -- as would be the case in the present circumstance of the dollar -- when the idea is to bring its value down.

In recent weeks, as the trade crisis mounted, congressional Republicans as well as Democrats have been pressing not only for specific bills to protect U.S. jobs, but also for action that would link the problem of the dollar to the trade issue. The situation has been exacerbated by greater public perception that the United States, as a consequence of the combined effects of the trade deficit and large capital inflows triggered by high interest rates, has for the first time since World War II become a debtor nation.

Although the dollar has dropped below its peak levels in February, it has begun to edge back up in the last month. After dropping in value by about 15 percent, it now is off only about 11 percent from the February high mark. Most economists say that the dollar is overvalued by about 30 percent on the average, which means that American exports, compared with the competition, are overpriced by about that much and that imports have that much of an advantage.

It was unclear yesterday just how far the United States is prepared to go in efforts to reduce the international exchange rate of the dollar. A suggestion by Japan that it place export controls on capital outflows to strengthen the yen reportedly has been rejected by the United States. But experienced observers said that financial markets likely would be disappointed if the dramatic announcement of an unexpected session of the G-5 took place with few concrete results.

As an indication of the unusual importance placed by the United States on the one-day session, the Treasury said that a formal statement would be issued and a press conference held by Baker at the end of the session. Economists here and New York said yesterday that the ministers should emphasize that the huge U.S. trade deficit -- running at an estimated rate of $150 billion this year -- is due primarily to an overvalued dollar, and that there can be little shift in the trade picture until there is a "realignment" of the dollar. These economists argue that the time is ripe for a drive to get an appreciation in the Japanese yen and the West German deutsche mark, because economic expansion is proceeding in those countries, while the American economy has receded from the strong 6.8 percent growth year of 1984.