Here's what freshly fired Treasury secretary W. Michael Blumenthal is going to do now that he's unemployed: play tennis, redecorate his new Watergate apartment, take a vacation and put a sickly social life back in order.

"i always wondered whether people went out with me because I was Michael Blumenthal, Treasury secretary, or Michael Blumenthal, me," he said when people say 'Yes I'll go out with you,' I'll know it's because it's me. I don't think a former Treasury secretary is very exciting."

Blumenthal was having a freedom lunch of sorts at Washington's traditional eating and drinking haunt for the political in-crowd. No matter that he's on his way out; maitre d' Pierre Sosnitsky fawned just the same.

"he was very friendly when he came in, and he said 'Hi, Pierre,'" said Pierre, who seated Blumenthal and his lunch date, Assistant Treasury Secretary (for Public Affairs) Joseph Laitin, under a copy of Renoir's "Le Moulin de la Galette." They had requested a quite corner, he said.

Blumenthal, skinny and pale was dressed in his usual benignly unfashionable manner: gray plaid suit, pink shirt and narrow red tie. The restaurant was hot, but Blumenthal, refusing to respond to the Washington summer clothing fad of less as better, kept his jacket on.

He and Laitin began with Bloody Marys. "i'm enjoying myself very much and I feel good," Blumenthal said. "Like I said yesterday, it's like taking out a parole with time off for good behavior."

But Blumenthal insisted the lunch wasn't a released-from-the-White House celebration. Business, he said, pure business. Problems. Transistions. The economy.

Nonetheless, between his tomato salad appetizer ($2.50) and his cold lobster with lemon ($11.75), a bottle arrived in a big silver ice bucket. It was compliments of Nancy Reynolds, vice president of Bendix Corp. and a Sans Souci luncher who had spotted Blumenthal and laitin in the corner. Before he came to Treasury, Blumenthal had headed the corporation.

"i can't remember the last time I had champagne for lunch," said Laitin as he sipped from his glass. He probably won't remember it this time either, since what he sipped was actually the house wine, Cuvee Sans Souci ( $12).

As for Blumenthal, he sipped the complimentary wine, smoked one of his trademark cigars, and accepted superlatives from the small handful of people who trickled, one by one, to his table.

"you were right on everything about the economy," said Lester Hyman, a partner in the law firm of Leva, Hawes, Symington, Martin and Oppenheimer.

Blumenthal thanked him graciously, then returned to his tomatoes and an evaluation of Federal Reserve Chairman G. William Miller, his just-picked successor.

But what about the other choice everybody's talking about -- that of Hamilton Jordan as the president's chief of staff?

"no comment," he said."I'm still the secretary of the Treasury and I'm not out to make negative comments about anybody. That is not proper and I want to do these things with a certain amount of grace."

He also hadno negative comments about Jimmy Carter, the boss who praised him 2 1/2 years ago and fired him 21/2 days ago.

"there's no bitterness or anger," Blumenthal said."the president is in good shape. He's doing what he thinks is right to lead the country."

And as for Blumenthal's lunch date, Laitin?

"i'm going to look for a new job and a new boss," Laitin said. "I suspect I'm on the endangered species list." CAPTION: Picture, Michael Blumenthal, by Margaret Thomas - The Washington Post