During their fifth Christmas at the White House yesterday, Nancy Reagan gave her husband a blue sport coat so he can maintain his place on the best-dressed lists. The president surprised his wife earlier this month with a King Charles spaniel puppy named Rex, and yesterday she in turn presented Rex with a red sweater, as well as a leash sporting a black bow tie for dressier occasions. The Reagans' gifts this year were a bit less utilitarian than previous yuletide presents, which have included a chain saw and a pickup truck. The Reagans leave tomorrow for California for a one-week New Year's vacation. Beach Boys Lose $5 Million Suit

Beach Boys Mike Love, Al Jardine and Bruce Johnston didn't appear in court last week, and they may have to pay a high price -- $5.4 million awarded to three Clark County, Wash., sheriff's deputies. A Portland, Ore., newspaper has reported that the three deputies claimed they were battered and falsely imprisoned when they were stopped from taking photographs at a Beach Boys concert in Portland on Nov. 9, 1981.

Each plaintiff was awarded $300,000 in general damages and $1.5 million in punitive damages after a brief appearance before Multnomah County Circuit Judge Mercedes F. Deiz on Dec. 19, the newspaper said. A default judgment had been entered against the musicians in August 1984.

The Beach Boys did not appear at the hearing or file papers contesting the lawsuit, the newspaper said. Court documents indicate that the Beach Boys, who played at the 1981 concert, were served with copies of the complaint at another concert in Portland in February 1983. A Christmas Jackpot

Lloyd Christie of Queens, N.Y., had the wish of a lifetime come true Tuesday when he won a Lotto jackpot of $10 million. Christie, 50, was the only person to choose all six winning numbers in Saturday's New York State Lotto 48 drawing, state officials said.

Christie said he angered his wife by making a last-minute trip to buy $5 worth of Lotto tickets, "because I wasn't sure if I had played my regular numbers. When I got home my wife said, 'You shouldn't have spent the $5. You have enough tickets.' " Christie said he spends between $40 and $60 a week on Lotto. Now his wife Nilva is not so annoyed. She said, "Santa Claus came early this year."

The couple said they had no immediate plans for the money, and Nilva Christie doubted their seven children -- ranging in age from 20 to 29 -- would find extra goodies in their Christmas stockings. "I have no money to buy Christmas presents," she said. "They haven't given me the first check yet."

The prize money will be paid in 21 installments of $476,190 each, with the first payment due in two weeks, lottery officials said. Christie said he bought the winning ticket Thursday and forgot about it until after the televised drawing. End Notes

Singer Peggy Lee, suffering from complications after double-bypass heart surgery 12 weeks ago, spent Christmas Day in a Santa Monica, Calif., hospital bed but was expected to go home before New Year's Day. "She is making satisfactory progress and will be released in the near future," a spokesman said. Lee, 65, underwent the heart surgery Oct. 7 in New Orleans and was operated on again two weeks later when an infection developed. She was flown to the Santa Monica hospital Dec. 9 for treatment of complications from the surgery . . .

Robbers near Los Angeles hijacked a truck earlier this week filled with 31 tons of frozen chicken donated to a police food drive. But when news got out that the drive had been seriously endangered by the chicken thieves, dozens of concerned people donated 13 tons of poultry, ham and canned goods. "One man came down and gave us 40 chickens," said Ty Reid, president of the San Diego Police Officers Association. The food drive started Nov. 25 with a goal of 50 tons of food . . .