"My evening was made when I walked in and there was Anatoliy Dobrynin going through the receiving line," said Sen. Charles Percy (R-Ill.) at the Chinese Embassy last night.

It also made the evening for China's new ambassador to the United States, Zhang Wenjin, who opened the doors of the embassy last night for his official Washington coming out. The arrival of Soviet Ambassador Dobrynin set the cameras to clicking and Zhang and Dobrynin to grinning. Then a photographer called Percy, chairman of the Senate Foreign Relations Committee, into the picture. Cameras clicked again. "I want 10 copies of that!" Percy called out with a laugh.

"I'm going to have that picture of us put up in the Foreign Relations Committee room as a symbol of togetherness," he said. "If the U.S. can bring China and Russia together, they can bring the Middle Eastern states together."

Like any new host bowing into a town known for parties that serve up juicy food and politics at the same time, Zhang was nervous. "Yes, a little," he said, chuckling. But he's already indicated he intends to do more entertaining than usual for the embassy, and last night's party was not a bad start.

"I'm happy to have so many good friends here," he said, smiling as nearly 400 guests trooped through the receiving line to greet the ambassador and his wife, Zhang Ying.

Zhang, who presented his credentials to President Reagan two weeks ago, wore a tailored brown suit with a small yellow flower embroidered on a lapel. His wife wore royal blue silk.

The embassy's 10 cooks had outdone themselves. Under chandeliers there was a dazzling array of food, perhaps 30 yards worth of table laden with sumptuous delights. Groups of dishes were repeated at the floral arrangements that graced the table--dumplings, beef rolls, duck, chicken, Chinese cabbage, Chinese cake; yellow gladioluses; dumplings, beef rolls, duck . . .

On another table, there was liquor--China Tunghua wine, Cheefoo White Wine, Chinese brandy, Kweichow moutai (a clear liquor that throttles the throat and should probably not be consumed anywhere near a match) and beer.

"Do you have Chinese beer?" asked one American woman.

"No. This is American beer," replied a Chinese waiter with a little smile.

"No Chinese beer?" she sighed.

There also was practically no tennis talk. But Chinese officials such as Shu Zhang, the embassy's first secretary, said they were happy to answer all questions about Hu Na, the 19-year-old Chinese tennis star who successfully petitioned for political asylum in the United States.

"I feel very sorry about the decision of the U.S. government," said Shu. "She's a young girl; her parents wish her to come back. It is very bad for the U.S. administration to have granted asylum."

Earlier, cameras also clicked when former secretary of state Alexander M. Haig Jr. arrived looking hearty and relaxed. "Well, I wouldn't have missed it," Haig told one Chinese official who greeted him. On his heels came Secretary of Defense Caspar Weinberger. More cameras and pictures in the receiving line and then Haig and Weinberger were standing with each other for pictures.

"Hello, Al," said Weinberger with a chuckle.

"Another tough day . . ." murmured Haig with a grin.

"This is a nice crowd," said Weinberger. "The ambassador seems to be enjoying his first days."

"You're very fortunate to have this new ambassador," Haig said to Chinese defense attache' Xu Yimin.

"You've met him?" said Xu.

"I know him," said Haig. "I'm very pleased. I hope it will keep relations better--not worse," said Haig, pointing his index finger for emphasis, "better."

Haig said of himself, "I've never been better. My tennis game has improved, and my disposition is great."