Former NATO commander Gen. Andrew J. Goodpaster, acting as a special emissary for the Carter administration, met here today with Argentina's foreign minister for the second time since he arrived last night to seek cooperation in a U.S. grain embargo against the Soviet Union.

Goodpaster's unannounced and hastily arranged visit comes at a time of growing recognition in Washington that Argentina's refusal to participate in the embargo -- in part of its irritation with continuing U.S. criticism of its human rights record -- could undermine efforts to punish the Soviets for their invasion of Afghanistan and press for their withdrawal.

The Carter administration and the U.S. Congress have not only criticized the military government for human rights violations, but have ended military assistance agreements and sales as a result.

Although a Carter administration official said today in Washington that the United States will not trade its human rights policy "for cooperation in grains," Argentine sources said their government would undoubtedly ask Goodpaster "what's in it for us" should Argentina agree to support the embargo.

Argentina has refused to stop its sales of grains and soybeans either to the Soviet Union or to third-party countries, such as Hungary and Poland, who are believed already to be buying on the Argentine market to supply the Soviet Union.

U.S. Under Secretary of Agriculture Dale E. Hathaway, told the Senate Banking Committee yesterday that the adminstration is "worried by Argentina's response" to the U.S. request that it "not take advantage of the partial embargo by increasing its sales to the Soviet Union to offset the 17 million metric tons of grain denied the Russians two weeks ago by President Carter.

Reuter news agency today quoted a State Department sources as saying that the administration had "realized too late Argentina's importance in the world grain market." The U.S. Embassy here estimates that Argentina will have an exportable crop of more than 12 million metric tons of feedgrains this year, enough to compensate substantially for the grain embargoed by the United States.

Initially, the Agriculture Department in Washington assumbed that Argentina would not be in a position to supply much of the Soviet demand because it was believed that Argentina's traditional grain customers would take most of this year's crop.

But according to one Western ambassador here, it now appears that virtually all of Argentina's 12 million tons could find their way to Russia. He explained that Argentina's traditional buyer's are rushing to buy American grain, which is cheaper because of a drop in prices after Carter's initial announcement of the embargo.

Corn, for example, was selling today for $10.75 per 100 kilograms (220 pounds) in Chicago while it was selling for $14 per 100 kilos on the Buenos Aires grain exchange. The differential is even greater when shipping costs are taken into account.

Goodpaster's mission will be made more difficult because it is understood that the Carter administration, while it wants Argentine cooperation with the boycott, is not prepared to resume arms sales, mute criticism of human rights violation's here or resume sales of enriched uranium until Argentina ratifies a Western hemisphere treaty barring nuclear weapons.

Nonetheless, several diplomatic observors said the general was a brilliant choice as the president's special representative because he is dealing with a highly conservative military government that is uncomfortable with its increasingly close ties to the Soviet Union. Those ties appeared to be reinforced by the decision to continue selling grain to the Soviets despite their invasion of Afghanistan.

Lt. Gen. Goodpaster, 64, a former supreme allied commander of NATO, is now superintendent of the U.S. Military Academy at West Point. He served as a National Security Council adviser during the Eisenhower administration.

Despite an almost reverential respect accorded Goodpaster today by the Argentine press, he will face an uphill battle in convincing the Argentines to limit their grain sales to the Soviet Union if he is unable to offer something tangible in return, according to diplomatic observers.

Argentina's determined independence from outside pressure was illustrated again today, even as Goodpaster was meeting with the foreign minister, Gen. Carlos Washington Pastor, and Economy Minister Jose Martinez de Hoz. The military head of Argentina's Olympic Committee said this country will participate in the Moscow games as planned.

Two high-ranking Hungarian diplomats arrived here yesterday, shortly before Goodpaster, another sign of the closer, if reluctant, ties between Argentina and the Soviet Bloc.