The world's major grain-exporting nations reached a historic agreement yesterday in support of a partial U.S. grain embargo against the Soviet Union.

Argentina, Australia, Canada and the nine-nation European Economic Community (EEC) promised that they "would not directly or indirectly replace" the 17 million metric tons of grain that President Carter has refused to sell to the Soviet government.

Announcing the pact after all-day negotiations among export representatives at the State Department, Agriculture Undersecretary Dale E. Hathaway insisted that it did not signal the birth of a new international grain cartel along the lines of the oil exporters' organization.

"I would not call this a cartel. I would never suggest that this is a cartel," he said. "It is a group of interested exporters that have a common concern and are taking specific action in response to this concern."

Among them, the 13 nations expect to have 163 million tons of grain available for export this year, nearly 90 percent of the world total. If the agreement sticks, it will be all but impossible for the Soviet Union to replace its lost 17 million tons from the remaining world supply.

President Carter ordered the partial U.S. embargo Jan 4 in response to the Soviet action in Afghanistan. While Australia, Canada and the EEC immediately expressed some support for the action, Argentina hesitated. The military government at first refused to take part in the freeze, but hinted that it might be persuaded in return for some softening of U.S. criticism of its human rights situation.

Hathaway said the human rights issue was not discussed in yesterday's meeting. The Argentines, he said, "were very strongly persuaded by our case."

The formal announcement devoted a paragraph to Argentina's position. Despite Agentina's previous public statements, the announcement said, "in this meeting the delegation of Argentina has stated that in no case does the government of Argentian intend to take trade advantages from the present international situation. Neither will it seek to alter artificially the current demands of the different markets."

Argentina is expected to have 13.7 million tons of grain to export this year, an amount that could have greatly eased Soviet pain over the U.S. cutoff.

Asked what the United States had promised in return for the agreement, Hathaway replied: "Each country recognized that this was not being done for the United States but on behalf of the western world." He said the mood of the meeting had been "strongly supportive" of the U.S. position.

Argentina earlier had refused "to be bound by measures and reprisals decided upon without consultation . . . or reached in centers of decision far from our country." Involvement in yesterday's talks apparently satisified that objection.

The embargoed wheat, soybeans and corn were intended by the Soviet government for use as cattle feed as part of a broad effort to increase meat supplies for its population. Hathaway said meat exports were not discussed at yesterday's beeting, although some Common Market nations had been expected to increase such shipments to the Soviet Union.

A major part of the day's talks involved "an extended and extraordinarily useful discussion" of U.S. steps to support domestic wheat prices by government purchases, Hathaway said. The prospect of 17 million metric tons of unsold grain initially had sent prices for future harvests plummeting on world markets, but the markets appeared to stabilize Friday.

The agreement includes establishment of a "group for the purposes of examining trade flows on a continuing basis in order to accomplish our common purposes." It also involves an agreement by the export delegations to reconvene "as necessary to review the situation" but Hathaway refused to discuss any possible dates or schedule.

Although the United States has taken steps to reduce exports of high technology equipment to the Soviet Union, it did not ask the other nations to do anything other than keep from replacing embargoed U.S. grain in Soviet markets, Hathaway said.

However, he noted, they are "reviewing their positions" on grain shipments they have already agreed to make and are considering "a whole range of actions" on existing commitments.

Hathaway said the pack would have no effect on any emergency food aid programs for underdeveloped nations or on U.S. plans to set up a grain reserve for such programs. Plans for the reserve "were not new to the rest of them," he said.

A previously scheduled meeting of Common Market foreign ministers is expected to ratify the agreement today in Brussels, Belgium. The EEC includes Great Britian, the Netherlands, France, Italy, Luxembourg, West Germany, Belgium, Ireland and Denmark.