President Reagan's two nominees to the International Trade Commission have run into trouble on Capitol Hill, partly because they gave the wrong answer to a key question about what the trade law says.

"They didn't even know the catechism," complained one trade lawyer who sat through their recent Senate Finance Committee hearing.

In addition, one of the nominees acknowledged during the hearing that although she was named to fill a slot that by law must go to either a Democrat or an independent -- but definitely not to a Republican -- she had worked on the Reagan transition team.

As a result, Finance Committee Chairman Robert J. Dole (R-Kan.) recessed the Dec. 8 hearing after only 40 minutes of questioning, and the two nominees -- Enrique Leon and Susan Wittenberg Liebeler -- were told to submit written answers to questions that some senators still had. Finance Committee sources said it is unlikely the committee will act on their confirmation before Congress adjourns.

One of the key Republican senators on trade issues, John Heinz of Pennsylvania, was described by an aide as being "very upset" at the lack of knowledge displayed by Leon and Liebeler. He said Heinz has not made up his mind on whether he will place a hold on their nominations

The key question that they both missed was whether the 1979 trade law set a higher standard for demonstrating injury from unfair trade practices than the earlier law did.

Leon, a Cuban-born professor of international finance at Fairleigh Dickinson University and professor of management at Pace University, answered unequivocally that the standard had been set higher in the 1979 law.

After long discussions with Heinz and Sen. Daniel P. Moynihan (D-N.Y.), Liebeler, a law professor at Loyola Law School, also gave that answer.

They both were wrong -- the standard remained the same.

Both professors were sent back to their books with lists of questions submitted by the senators. The two nominees set up offices in the ITC, and, according to sources there, used the resources of the commission to help get their answers straight.

Liebeler acknowledged under questioning by Sen. Russell B. Long (D-La.) that she had worked on the Reagan transition team for Michael M. Uhlmann, who now is a special assistant to the president in the White House office of policy development, and as a special assistant to Securities and Exchange Commission Chairman John S.R. Shad. She also said she had supported Reagan's presidential nomination.

But she insisted that she is politically independent and that she was picked for the transition team because of her expertise in security regulation.

By law, the seat to which she was nominated cannot go to a Republican since the six-member ITC is supposed to be a politically independent, quasi-judicial body free from White House pressure. (That problem did not arise with Leon, a Republican who was named to a seat that could be occupied by a Republican or an independent.)

According to Senate sources, both Leon and Liebeler have received closer scrutiny than most ITC nominees because they are largely unknown in Washington trade circles. Previous nominees to the six-member panel generally have come from Capitol Hill, where they had built a clear record on trade issues, or they have had the strong support of a key senator involved with trade matters.