Protesting U.S. agricultural-trade policy, Sen. Kent Conrad, D-N.D., said he will block the confirmation of Jeffrey Garten as undersecretary of Commerce, further clouding prospects for the nomination.

At a hearing before the Senate Finance Committee, Sen. Conrad criticized a

draft farm-trade accord with Europe as an "attack on the American farmer" and said Mr. Garten did not understand the threat posed by foreign agricultural subsidies.As evidence of this, he waved a 1992 article by Mr. Garten in the magazine Foreign Affairs, which advised then President-elect Clinton to accept an ''imperfect" deal on agriculture to obtain a broader world-trade deal in the Uruguay Round of talks. More important for the United States, he said, were gains on freer trade in financial services, fewer investment curbs and better protection overseas for copyrights and patents.

''If there is a good time for Clinton to fight the farm lobby, it is at the beginning of his term," Mr. Garten wrote in that article.

In an interview after the hearing, Sen. Conrad confirmed that he would ''put a hold" on Mr. Garten's confirmation by the Senate, using an informal rule that allows any senator to block action on a nominee.

"I informed the chairman (Sen. Daniel Patrick Moynihan, D-N.Y.) that I did intend to put a hold on the nomination," Sen. Conrad said. "I would like to hear some explanation from Mr. Garten on his comments and some recognition

from the administration that we seem to be heading into an agreement that will permit other countries to continue subsidizing and steal our markets."

Although the Commerce Department does not take the lead on agricultural issues, Mr. Garten would sit on a key interagency committee that makes most trade-policy decisions. "We've lost many times in that process," the senator said.

Sen. Conrad said that a November 1992 agreement with the European Community will allow EC governments to continue massive farm subsidies that drive down commodity prices and displace American farm exports. The agreement calls for cuts of between 24 percent and 36 percent, but does not adequately restrain European export subsidies, he said.

It is not unusual for a senator to briefly hold up a nomination to make a point, but Mr. Garten has the added problem of a challenge from Sen. Donald Riegle, D-Mich., chairman of the Senate Banking Committee and a powerful critic of Japanese trade practices.

The Banking Committee, which must also approve Mr. Garten before his nomination can be sent to the full Senate, has yet to even schedule a hearing. Sen. Riegle, who is leading opposition to the North American Free Trade Agreement in Congress, is reportedly dismayed by Mr. Garten's work in 1991 as a high priced "adviser" for Japanese car giant Toyota.

Commerce Secretary Ron Brown has had an unusually difficult time getting his top aides nominated and confirmed, suggesting that the department's traditionally weak role in making trade policy has been further undermined in the Clinton adminstration.