American and Common Market trade officials agreed here today on a four-phase negotiating scheme designed to break the deadlock in the multilateral trade talks in Geneva.

U.S. Special Trade Representative Robert S. Strauss hailed today's session as "the most significant in the history" of the four-year old trade talks, called the Tokyo round because they were launched in the Japanese capital.

Strauss said that American and European trade experts were committed to settle key differences "on or before January 15" and hoped to have a nearly complete package meshing the four phases of negotiation by April 15.

Emerging from seven hours of intense discussions in an ebullient mood. Strauss asserted that "for the first time in this round, a joint political commitment" to achieve more liberal trade objectives had been reached by the United States and the European Community.

"This is the finest day I've had in this job," he boomed. He said he would hand in "an exceedingly positive report" to President Carter.

Both Strauss and the European Community's External Affairs Commissioner, Wilhelm Haferkamp, claimed the world "could not afford the luxury of delay" in seeking to spur freer world trade as unemployment climbs in the West and countries are tempted to resort to protectionism to curb foreign imports.

"We are convinced that the world economic situation requires active and speedy progress to complete the trade negotiations," Haferkamp said.

The timetable obliges the United States and the European Community to establish a host of ground rules within 6 months on prickly negotiating topics that have stymied progress at the General Agreement on Tariffs and Trade (GATI) talks for nearly a year.

In the initial phase, both sides expect to devise a general framework that includes a formula for tariff cuts and ways to handle agriculture issues in the trade talks. They also hope to agree on how to broach the problems of developing countries, as well as what commercial tactics should be adopted to treat nations that do not wish to adhere to the tariff formula.

Some weeks later - under phase two - the United States and the Common Market would submit proposals for three areas - tariffs on farm trade, other obstacles to trade grouped under the heading "non-tariff barriers" and levies to be placed on countries not participating in the tariff formula.

Phase three would involve drawing up texts to incorporate various trade issues under codes that would bind all GATT signatories.

The final phase would entail working out industrial tariff schedules and haggling "item-by-item" over offers and exceptions to agriculture trade with mutual approval slated for "no later than Jan. 15."

"The total package would then be in place for final, detailed negotiations, which - give or take - should be concluded within 90 days," Strauss said.

"If everything goes according to plan, we'll have a GATT round of substance next spring that will cover the next decade of trade relations," he added.

Launched in Tokyo in September, 1973 with the stated intent to reduce non-tariff obstacles to trade and improve freer trade prospects for farm goods - two issues neglected by the Kennedy round of the 1960s - the GATT multilateral trade talks were stalled by the delayed congressional passage of the U.S. Trade Act. Actual bargaining in Geneva did not begin until February 1975.

But the trade negotiations soon ran into other snags - notably the protracted dispute between the United States and Europe over Liberalized farm trade, the Common Market remained suspicious of U.S. proposals that threatened the EEC officials often retorted that the United States racked up farm trade surpluses with Europe and did not require improved access to markets.

Since the U.S. election campaign last autumn, the trade talks were held in abeyance until the new administration settled into office and charted its trade policy.

Strauss said today that the Carter administration had no intention of disrupting or changing the "structural situation" of the Common Market's farm policy, but negotiations to liberalize agricultural trade must occur "in parallel" with talks on industrial trade issues.

"Agriculture is still on the front burner with industry," he said.

Strauss also tried to allay European worries over President Carter's recent decision to guarantee U.S. maritime unions 10 per cent of oil import trade.

"The U.S. Congress asked for a 30 per cent cargo preference but that plan was vetoed," he said. "We originally had only wanted 5.5 per cent rising to 9 per cent over five years."