The chairman of the House Ways and Means Committee's trade panel yesterday questioned the impartiality of two Reagan administration appointees to the International Trade Commission and said their philosophical biases may prevent them from complying with U.S. trade laws.

In a letter to Paula Stern, head of the ITC, Rep. Sam Gibbons (D-Fla.) singled out Susan B. Liebler, the ITC vice chairman, who has been on the commission for two years, and Anne E. Brunsdale, the latest Reagan appointee, who joined the ITC in January.

Liebler, a political independent who served on the Reagan administration transition team, is believed to be the president's choice as the next head of the ITC.

The issue is important to Congress, which sees the quasi-judicial ITC as a key federal agency for determining whether American companies and industries get tariff or quota protection on grounds they have been hurt by unfair trade tactics of other countries. Gibbons asked for a response to his letter by Friday so it can be considered next week when the Ways and Means Committee writes a broad-based trade bill.

Critics said the two Reagan appointees were reaching conclusions unfavorable to U.S. companies seeking trade relief from the agency, and were basing such findings on their own interpretation of the law instead of following Congress' intent.

Gibbons sent his letter after a representative of steel pipe and tube interests, Roger B. Schagrin, complained in testimony Friday that the two Reagan appointees were using "novel approaches . . . which may not be in accordance with the statutory mandate or congressional intent" of trade laws, Gibbons wrote.

Rep. Donald Pease (D-Ohio) echoed Schagrin's concern, suggesting that Liebler and Brunsdale were ignoring statutory guidelines on whether companies have been hurt by surging imports.

Another commissioner, Alfred Eckes, raised a similar question in a dissenting opinion in a recent trade case. And House and Senate staff members who specialize in trade issues said they also have received complaints about the reasoning used by Liebler and Brunsdale in their opinions.

Gibbons said "the gist of the testimony" at the hearing Friday "was that the philosophical tenets and unconventional methodology . . . are clouding their ability to properly administer the trade laws in an impartial manner."

He called these charges "very disturbing," especially because Congress is in the process of toughening U.S. laws against unfair trade practices. "Tougher trade laws may be meaningless if the tougher laws are not being administered by the commission in the spirit in which they were enacted," Gibbons said.

In another trade move yesterday, U.S. Trade Representative Clayton Yeutter tried to turn around a bipartisan majority of the Senate Finance Committee that lined up last week against giving the Reagan administration authority to negotiate a free-trade pact with Canada.

He asked the Electronics Industries Association, which is holding its spring meeting here, for help in lobbying committee members, and said high-technology industries in the United States would gain from free trade with Canada. Then he rushed off to a White House meeting to develop an administration strategy to gain support before a committee vote scheduled for Thursday.

On Friday, 14 of the 20 members of the committee said they oppose giving the Reagan administration the negotiating authority it wants. The senators said their opposition stems from frustration over administration trade policies and concern that U.S. interests in sectors such as lumber, pig and cattle farming, potatoes, fishing and steel would not be properly protected in the negotiations.

In Canada, meanwhile, Trade Minister James Kelleher said the senators "sideswiped" his government by lining up against the pact, and he warned that Reagan's credibility is at stake in the trade issue, according to United Press International.

He said Reagan assured Prime Minister Brian Mulroney at a summit in Washington last month that the trade talks would proceed without any preconditions.

The Reagan administration had pressed the free-trade pact with Canada as a possibile alternative if efforts to get a new round of global trade talks started this year failed. Third World nations, headed by Brazil and India, oppose the new round and have been working to stall it.

Preparations for the global round are under way in Geneva, where the General Agreement on Tariffs and Trade yesterday announced that Punta del Este, Uruguay, will be the site of the September ministerial meeting that will kick off the new round.