Romania has failed to pay the Commodity Credit Corp. $5.8 million it owes for U.S. agricultural products, becoming the second Soviet-bloc country, after Poland, to go into arrears in its debts to the U.S. government.

Officials at the corporation, the Department of Agriculture's bank, said yesterday that checks are to be sent this week to reimburse two New York-based banks handling the collection of the money due from Romania on government commodity loans.

Under a routine financial procedure, First Chicago International and the European-American Bank transferred the funds to the CCC on the dates the money was due. But when the banks were unable to collect from Romania's Bank for Foreign Trade, they notified the CCC and asked for their money back.

"It's pro forma. We are under a legal obligation to the banks," said Deputy Undersecretary of Agriculture Thomas A. Hammer. "I would imagine that the next step is for someone at the State Department to go talk to the Romanians."

The latest development in the unfolding financial crisis in Eastern Europe raises the prospect of a new political embarrassment for the Reagan administration, which is already facing criticism for allowing Poland's military regime to delay paying its debts.

Defense Secretary Caspar W. Weinberger and some congressional officials have argued that permitting such delays reduces pressure on the Soviet Union to cover financial obligations of its satellites. But President Reagan has overruled a formal declaration of default against Poland on grounds that it would remove remaining U.S. political leverage on Warsaw's virtually bankrupt military government.

Although Romania, like Poland, is a member of the Soviet-dominated Warsaw military pact, its foreign policy is considered the most independent in the Soviet bloc, and the United States has supported its economic development. Nevertheless, the nonpayment could increase pressures in the administration against any new U.S. "bail-out" in Eastern Europe.

U.S. officials yesterday appeared surprised by the development. Hammer said he was not aware of the arrearages, which were detailed by CCC financial officials.

On Secretary of State Alexander M. Haig Jr.'s trip to Bucharest two weeks ago, Romanian officials reportedly sought promises of a new $65 million CCC loan to buy corn and soybean meal, but President Reagan rejected that request last week.

Romania owes the United States $91.3 million this year under old commodity buying loans. Of that, $41.5 million is owed directly to the CCC, with the collection handled by private banks. The rest is owed to private banks but is guaranteed by the CCC.

The uncollected $5.8 million is in the first category. On Jan. 30, First Chicago International notified the CCC that it could not collect $319,128.65. On Tuesday, European-American Bank advised the agency that Romania had not paid $5,465,259.54 due in December and January.

Private banking sources confirmed last week that Romania had fallen behind by as much as $1 billion in payments to its private bankers and creditors and was seeking to arrange a "limited rescheduling" of its hard currency debt, believed to total between $10 billion and $14 billion.

The International Monetary Fund suspended Romania's right to draw new credits last November and reportedly is insisting on substantial reforms in Romania's rigid, Soviet-style economy as a condition for continued financing.