The United States is likely to miss the Jan. 1 start of a global system of classifying products for tariff purposes, a prospect that has sparked an exchange of charges between the Reagan administration and Congress over who is to blame.

The administration, pressing to get legislation implementing the new system passed before Congress adjourns for the year, accuses the Democratic leadership of holding the measure hostage in an effort to get White House cooperation on the trade bill. Legislation implementing the system is part of the trade bill being worked out in a House-Senate conference, but action on the bill, expected to be completed by now, has been put off until early next year.

Republican and Democratic lawmakers, saying that it is too late in the session for Congress to act, accused administration trade officials of ignoring the tariff issue all year.

"They {administration officials} totally neglected it all year. We took the initiative to get it in the trade bill. All of a sudden they are in heat over it," said Senate Finance Committee Chairman Lloyd Bentsen (D-Tex.), who has borne the brunt of the administration's wrath.

Twenty-five members of the House Ways and Means Committee asked Chairman Dan Rostenkowski (D-Ill.) yesterday to move legislation approving the new tariff system. On the Senate side, Sens. Robert Packwood (R-Ore.), the ranking Republican on the Finance Committee, and Spark M. Matsunaga (D-Hawaii), the head of its trade subcommittee, have offered to try to get a unanimous consent agreement to allow consideration without any amendments. Packwood had asked Bentsen to include the new system in the continuing resolution or budget reconciliation measures.

Members of a broad coalition of business interests said they will be the losers in the delay. In letters sent to all members of Congress last week, the Joint Industry Group said the delay in joining the new global system, called the Harmonized Commodity Description and Coding System, will add to business costs and hurt the United States' ability to influence future changes. The system has been adopted by most major trading nations.

While the United States can join the system after Congress approves the legislation, administration officials and business leaders said a delay will keep this country from participating in the initial organizing meetings, which could set the tone for operation of the new system.

"The U.S. government and U.S. businesses have invested a lot of time and money in adapting to the new harmonized system," Alexander B. Trowbridge, president of the National Association of Manufacturers, said in a separate letter to senators. "If the harmonized system is not implemented on schedule, there will be additional expenses."

When House Speaker Jim Wright (D-Tex.) announced Nov. 19 that consideration of the trade bill would be delayed until early next year, administration officials started a low-key campaign to get Congress to remove the harmonized system from the bill so it could be passed on its own.

"Danny {Rostenkowski} and I both agree that it is too late to get it done," Bentsen said. The administration accused Bentsen of refusing to separate the harmonized system from the trade bill so he can use it to get President Reagan to sign the trade bill next year.

Other congressional trade specialists and some business leaders back Bentsen's view that the administration was slow to move on getting the harmonized system passed. The administration, for instance, didn't submit legislation until after the House had passed the trade bill, and sent a low-ranking official to testify before the Finance Committee.

"The administration really dawdled on this and now they are trying to blame us. If it had been up a year ago, it would have gotten to the floor," said a trade specialist for a House Democrat. The aide to a Senate Republican said, "All of a sudden they decided three weeks ago they want the harmonized system."

Assistant U.S. Trade Representative Roger Bolton said the administration adopted a low-key approach, working through business groups, to avoid a confrontation with Congress.

"Some people in Congress seem to think that the more the administration wants something the less likely they are willing to give it to us," Bolton said. He added that approval of the system is not something the administration wants but rather something business needs.