Political dissension clouded the 25th anniversary of the North Atlantic Treaty Organisation today (Thursday, April 4). At NATO headquarters in Brussels, ceremonies marking the founding of the fifteen-nation defence alliance were distinctly subdued.

Plans for major celebrations had been scrapped following the failure of the United States and NATO's European members to reach agreement updating the original NATO principles. The row reached its climax last month when President Nixon called off a planned trip to Brussels to sign a new transatlantic declaration of principles.

In the single speech at today's Brussels parade, NATO Secretary General Joseph Luns warned Europe not to let economic Differences with the United States disrupt the alliance. He also cautioned members against cutting defence expenditure because of the economic problems facing the west.