President Reagan has a showman's talent at his State of the Union addresses that the great introducer Ed Sullivan could have envied. At the past several addresses, the president has had mystery guests sitting with First Lady Nancy Reagan whom he introduces as American heroes. The first in 1982 was Lenny Skutnik, the hero of the 14th Street Bridge Air Florida plane crash. Last year he introduced Harlem mother Clara Hale and graduating West Point Cadet Jean Nguyen, a Vietnam refugee.

The White House has let it be known that Reagan will introduce two guests at his Jan. 28 speech, and since he likes to keep it a close secret to get the full drama, Capitol Hill staffs are speculating and making bets on who it will be. Most agree that one of the guests will be Uli Derickson, the stewardess credited with saving so many lives during the TWA hijacking. There's heavy betting on Marilyn Klinghoffer, the widow of murdered Achille Lauro passenger Leon Klinghoffer. One source says the time is right for him to introduce Martin Luther King's widow, Coretta Scott King. The White House is not speculating or answering questions on the subject. Woody Allen's 'Family' Flick

Woody Allen's new movie, "Hannah and Her Sisters," is a family affair. Not only does it once again star his lady Mia Farrow, but Farrow's mother, actress Maureen O'Sullivan, once Jane in the old Tarzan movies, plays her movie mother. Farrow's children are also in the film, which was previewed here this week. And much of the movie was shot in Farrow's New York apartment. That's one way to keep the budget well within budget.

It's also always refreshing to see Woody Allen's New York City, a place of both grit and glamor, when the California settings of so many movies and television shows make one long for anything without palm trees and sunshine. The film opens Feb. 7 in only two Washington theaters and no suburban ones. It is unfortunately the last opportunity to see Lloyd Nolan, the booming-voiced, widely admired character actor who died in September. End Notes

Wealthy Washington developer Alan Kay once planned to build a multimillion-dollar, 30,000-square-foot home on 2.5 acres on posh Foxhall Road next to the Belgian Embassy. That was before he shelled out some $4.25 million for Merrywood, the home owned by Nancy Dickerson and C. Wyatt Dickerson. The Foxhall property, now up for sale for $2 million, is said to be the most expensive lot ever offered for sale in the city . . .

Hotel changes: Washington native J.T. Kuhlman, who has been running the Hotel St. Anthony Inter-Continental in San Antonio, will be returning to the city to head the Willard Hotel, which will be the flagship of the Inter-Continental chain. His father, Thane Kuhlman, was deputy chief of protocol in the Kennedy administration . . . Richard Bichaku, better known as "Mr. Richard" at the 1789 restaurant where he was maitre d' for more than 10 years, will become maitre d'ho tel for the Jefferson Hotel beginning next month. He will be in charge of the Hunt Club restaurant and the hotel's food services . . .

Kansas Lt. Gov. Tom Docking was in town last night for a fundraiser at the Monocle Restaurant for his campaign for governor in this year's election. He is planning on becoming a third-generation Kansas governor. His father Robert was governor from 1966 to 1974 and his grandfather George from 1957 to 1961 . . .

Singer Andy Williams was stopped by the California Highway Patrol Monday for speeding and weaving in and out of traffic in his Rolls-Royce convertible. He submitted to a urine test and spent five hours in the San Bernardino County Jail. Blood-alcohol test results were not expected for several weeks . . .

Rex the White House dog, who is still recovering from his tonsil surgery, had his first public outing yesterday. He and First Lady Nancy Reagan strolled from the White House in the unseasonably warm afternoon to go to the Impressions card shop near the White House to buy valentines . . .

It seems to be official now. After all that talk and teasing at the Martin Luther King Jr. spectacular at the Kennedy Center, Diana Ross will marry Norwegian shipping magnate Arne Naess Jr. Naess said the wedding would be in a Swiss church on Feb. 1. There were no other details . . .