OTTAWA (AP) _ Canadian officials say they have urged Canadian businesses not to undermine U.S. sanctions announced this week against Libya, and that the government is considering further steps requested by the United States.

The officials denied late Wednesday a statement by an official spokeswoman that Canada would not side with the Reagan administration and consider economic sanctions against Libya.

President Reagan ordered the sanctions, which include freezing Libyan assets in U.S. banks, because of Libya's alleged role in fostering terrorism, including the Dec. 27 attacks at Rome and Vienna airports that left 19 dead and 120 wounded.

His call on allies for support of the new U.S. policy met little enthusiasm in Europe.

But Sean Brady, chief spokesman for Foreign Secretary Joe Clark, said Canada has been considering this week whether to expand its sanctions against Libya, and is considering a request presented Wednesday by U.S. Ambassador Thomas Niles.

Brady said Helene Lafortune, a spokeswoman in his department, misstated government policy Monday when she said any Canadian sanctions would have such little effect because of the minimal trade with Libya that they would not be considered. Clark and Brady were out of the country at the time.

Brady said Canada has had stiff restrictions on trade with Libya since 1969 because of Col. Moammar Khadafy's stance toward Israel and apparent encouragement of terrorism.

''We've already gone a long way,'' Brady said. ''The government is now considering whether further steps by Canada are in fact necessary.''

Clark told reporters Wednesday night after a meeting of senior members of Prime Minister Brian Mulroney's Cabinet that Canada has already done some of the things the United States is asking.

Canadian officials are urging Canadian businesses with operations in Libya ''not to undermine'' American actions, Clark said. He and Brady declined to be specific about other moves the United States would like to see from Canada and other allies.

Brady said Canada has long forbidden export of military equipment and sensitive techonology to Libya, does not have a resident ambassador and will not let Libyan students pursue courses in nuclear engineering and other fields with military potential at Canadian universities.

In the first nine months of 1985, two-way trade between Canada and Libya amounted to less than $100 million, but there are about 1,300 Canadians resident in Libya, many employees of Canadian subsidiaries of American companies.

Witold Weynerowski, the Canadian ambassador to Tunisia who also is accredited to Libya, was sent to Tripoli on Wednesday to talk to Canadian residents and Western diplomats and report immediately to Clark on the situation, Brady said.