By Chinese standards, the 35th anniversary of the founding of the People's Republic of China was a young one -- archeologists say the Chinese go back to the third millennium B.C.

In last night's drizzle, no firecrackers exploded -- but the pride of the Chinese diplomats lit up probably the most festive national day party the People's Republic has held here.

Chinese women, who a few years back wore dark cotton Mao suits, last night had on elaborate Chinese silk and velvet dresses, with red roses. Zhang Ying, the ambassador's wife, wore a gold and red brocaded jacket woven with the characters for long life.

A feast of Chinese delicacies, prepared by the 12 embassy chefs, was centered by huge flower arrangement.

And 750 diplomats and other dignitaries lined up to congratulate Ambassador Zhang Wenjin.

"For the Chinese people, the 35th anniversary is very important. All numbers with five or divided by 10 are significant," said Zhang Ying.

The dean of the diplomatic corps, Soviet Ambassador Anatoliy F. Dobrynin, came and "invited my husband to lunch," said Zhang Ying. "He said Mrs. Dobryin is still in Moscow."

Zhang said the Chinese here were proud of the two-hour parade held in Peking this weekend, which many watched Sunday on television at a noonday party for 500 Americans of Chinese ancestry.

Hu Ding Yi, deputy chief of mission, said, "This was our first big parade in years. Too much work. But this being the 35th, we wanted to have a big parade, a bigger reception here." He listed with satisfaction: "The Olympic sportspeople won so many gold medals, they had their own float in the parade. We have the historical Hong Kong agreement. We want to show the world we want to modernize and have economic prosperity, a peaceful time with a better life."

David Laux, who handles Asian affairs for the National Security Council, said the parade "showed that Deng Xiaoping is el supremo, it brought the People's Army back to respectability, and it emphasized the progress in economic conditions. The military weapons parade was not a threat, but showed they are prepared."

Commerce Secretary Malcolm Baldrige said the United States and China have $5.5 billion in trade. "They sell us more than we sell them. But that's because we already have a market for their textiles. As they modernize and need more heavy equipment, we'll sell them more."

Also congratulating the Chinese in a ballroom decorated with 1949-1984 in great gold figures were: John E. Reinhardt, the newly named Smithsonian director of International Ativities, which includes the International Center, now under construction; Catherine Shouse, Wolf Trap founder; Australian Ambassador Sir Robert Carrington Cotton, whose country has a big China trade; and French Ambassador Bernard Vernier-Palliez and his wife, Denise, who said they were leaving for France in November.

Watching guests, Wang Xiang, wife of the minister-counselor, said, "You love our food. We love your advanced technology."