Peking has marked today's first anniversary of Chairman Mao Tse-tung's death with its first open attack on slavish adherence to Mao thought, once unassailable dogman for all Chinese.

The post-Mao Chinese leadership also bluntly admitted that party officials have lied about conditions in China in order to square themselves with official policy.

In a long article in the theoretical journal Red Flag, Politburo member Nieh Jung-chen brough the new administration of Communist Party Chairman Hua Kuo-feng closer than it has come before to asserting its authority to change Mao-inspired policies.

Nieh's commentary, broadcast carlier this week by Radio Peking, suggests the government has new confidence in following its own pragmatic instincts in developing China's industry and does not feel bound by Mao's insistence on putting social concerns, like the need to climinate class differences, above economic considerations.

Nieh wrote that officials must stop glossing over the truth and must use Mao's thought only as a guide, not as a substitute for practical solutions to changing problems.

The article comes at the end of a year in which Mao's successors have made remarkable changes in his policies while insisting that they were following his instructions to the letter.

"To correctly apply Mao thought," says Nieh, a 78-year-old army veteran of the Long March, "we must master its spiritual essence, study is stand, views and methods, regard its basic theories as our guide to action, and firmly combat the tendencies to make use of a number of phrases . . . as dogma in order to disregard time, locations and conditions."

Since Mao's death Sept. 9. 1976, some of his closest desciples in the Polliburo, including his wife Chiang Ching, have disappeared. Scores of veteran party and army officials, like Nich, have returned to power after a decade in which their efforts to dampen Mao's enthusiasm for a classless society had made them politically suspect.

Traditional dramas, operas and art, shelved under Mao as insufficiently revolutionary, have returned to public view. Foreign trade, once said to violate Mao's policy of increasing China's self'reliance, is on the rise. Student attacks on teachers and worker attacks on managers, encouraged by Mao as part of the Marxist class struggle, have been discouraged in favor of discipline and production.

To justify these changes, Nieh used one Mao canon to undermine the rest. The late chairman's call for investigation of the facts becomes in Nieh's view a blessing for the pragmatic approach to China's problems that Mao derided in his later years.

"The objective world is full of contradictions and changes," Nieh says.

"Our thinking must realistically reflect such contradictions and changes. All correct ideas are subject to changes on the basis of time, location and conditions. Otherwise, they will become metaphysicial ideas."

"There are many problems that need to be solved on all fronts," Nieh said. If the leading cadres satisfy themselves with general calls and with a few quotations as the basis for such calls, they will not be able to solve problems.

"To persist in the style of seeking truth from facts," he added, "it is necessary to oppose empty talk and, especially, oppose the telling of lies. When Lin Piao [a former defense minister who allegedly tried to kill Mao] and the 'Gang of Four' were running amok, some comrades were afraid to tell the truth and even hypocritically told lies. "If, under the circumstances of that time, this was somewhat understandable, it is now very wrong to continue to tell lies. Whoever continues to do so is deliberately trying to do harm to the party, the country, the people and himself. Lies cannot last very long and will eventually be laid bare.