PARIS, April 27--Taking up his first foreign assignment as U.S. Secretary of State, Christian A. Herter arrived in Paris today to help shore up weak points in the Western front for Geneva talks with the Soviet Union.

Herter will begin formal talks with his French, British and West German counterparts tomorrow in the French Foreign Ministry. Diplomatic sources said the talks, scheduled to last three days, will be under three general headings: Berlin, German reunification, European security.

American and French sources professed optimism for a solid Western position before the East-West foreign ministers talks open in Geneva May 11. A highly informed American source said: "I'd be surprised if we didn't have it wrapped up beautifully before Geneva."

Liu Red China's President

TOKYO, April 27--Liu Shao-chi, 61, a Moscow-trained theorist with a reputation for getting things done, became president of Red China today. In succeeding to one of Mao Tze-tung's old jobs for a four year term, the tall, light-haired son of a peasant family strengthened his status as heir apparent to the Chinese Communist Party leadership that Mao, 65, retains in the Peiping hierarchy. Peiping radio hailed Liu as "a leader second only to Mao Tze-tung."