Treasury Secretary James A. Baker III and Deputy Secretary Richard Darman have canceled plans to attend a privately sponsored conference on monetary issues in Zurich on June 28 and 29 because of the pressure of other responsibilites, Treasury officials said yesterday.

But the more important reason for their decision was a reluctance to appear to be lobbying European government officials in a quasi-public forum on delicate matters that should be discussed in private negotiations, a senior official said.

He suggested that many of the invitees to the conference were from parties out of power in Europe, and that the effort in Zurich to achieve better macroeconomic coordination might therefore be counterproductive. "The Europeans worry a lot about the United States putting public pressure on them," he said.

The conference, cosponsored by Sen. Bill Bradley (D-N.J.) and Rep. Jack Kemp (R-N.Y.), will be attended by European, American and Japanese officials -- some drawn from parliamentary bodies -- businessmen and bankers.

The theme -- the promotion of exchange-rate stability -- was explored at a similar session in Washington in November.

David Smick and Richard Medley, the organizers of the Zurich conference, which is financed by corporate contributions, had solicited Baker's participation in the hope that he would use the private forum as a vehicle to advance the Treasury's efforts for international coordination, as outlined in May at the Tokyo economic summit.

But a Treasury official said yesterday that the current stage of carrying out the Tokyo decision focuses on numerous technical details not suitable for the meeting in Zurich.

A related reason offered by the Treasury was that the secretary felt he had to remain in Washington to stay on top of the tax-reform debate in Congress and of the potential economic crisis in Mexico.