Withdrawal of U.S. sanctions against the Soviet natural gas pipeline project has not resolved all the problems raised by their imposition, British Secretary of State for Trade Lord Cockfield said yesterday.

Although the withdrawal of the sanctions by President Reagan "is good news for us," the American assertion of a right to exercise its jurisdiction in Great Britain and other countries remains controversial, Cockfield said in a speech to the Institute for International Economics.

Cockfield, who is here for discussions with American trade officials before the end-of-the-month meeting in Geneva of the General Agreement on Tariffs and Trade, also said that, although the settlement last month of a steel dispute between the United States and the European Community was a relief, "We in Europe remain deeply unhappy about this whole episode."

He also said that expectations for success of the GATT meeting should be tempered by a realistic appraisal of the problems to be discussed, the chief one of which, in his view, is the lack of sufficient access to markets: the Japanese, the newly industrialized countries and more developed countries such as Australia and Spain.

Coincidentally, the International Institute issued a report on trade suggesting that the Japanese market "is much less closed than is conventionally believed." The detailed document called on the GATT ministers to place a freeze on the imposition of all new trade barriers to counter "the rising tide of protectionist measures."

Also yesterday, Deputy Treasury Secretary R.T. McNamar said the U.S. merchandise trade deficit could widen to "perhaps $75 billion" in 1983 from an estimated $40 billion this year. McNamar said the United States' leadership of a global economic recovery next year would cause the trade gap to widen.

Cockfield's complaint on the U.S.-EEC steel agreement was that the American government had adopted "extreme" interpretations of the subsidies paid by European governments, even though "the difficulties of the U.S. steel industry were not due to imports from Europe."

He suggested that the steel subsidies in Europe were a necessary "social cost" of restructuring an industry with excess capacity. On the other hand, he argued that the tax advantages given here to the Domestic International Sales Corporations -- the so-called DISCs -- amount to an export subsidy in clear violation of GATT rules.

The International Institute's report on trade policy not only called for a standstill on new restrictive trade devices, but for a new, multinational trade negotiation for the 1980s that would convert all existing nontariff barriers into tariffs, and then phase them out over time.

William Cline, a coauthor of the report with C. Fred Bergsten, said that the revenues from the increased tariffs could be used to provide additional "trade adjustment" compensation to finance worker relocation or retraining.