"Bloom County" cartoonist Berke Breathed, who underwent surgery after his ultralight plane crashed in New Mexico Jan. 22, is still hospitalized with additional complications. Bob Fenton, a spokesman at St. Joseph's Hospital in Albuquerque, said Breathed has developed a blood clot in his lung and is being treated with anticoagulants.

Breathed, who was expected to be released from the hospital today, is listed in fair condition and probably will be in the hospital another 10 days. Fenton said Breathed is expected to recover fully. The 28-year-old cartoonist suffered a compression fracture in his lower back because of the crash. He was operated on two days later and doctors inserted rods into his back. Birthday Gold

Nancy Reagan didn't give her husband a pickup truck or a manure spreader as she has for previous birthdays. Instead, in honor of his 75th, she surprised him last night with a $20 gold coin minted in 1911, the year of his birth. A coin dealer has estimated the coin's value at $450 to $600. When asked why not a manure spreader this year, the first lady replied, "The manure spreader is still new." It was a successful birthday: The president received at least three cakes earlier in the day, and by 6 p.m. yesterday his birthday card count was 8,138.

At a Senate prayer breakfast earlier in the day, the president continued his running jokes about the landmark day. "Seventy-five years ago," he said, "I was born in Tampico, Illinois, in a little flat above the bank building. We didn't have any other contact with the bank than that. Now, here I am, sort of living above the store again." End Notes

Lady Bird Johnson is reportedly in good spirits in St. David's Community Hospital in Austin, Tex., where she was admitted Wednesday after a fainting spell. She will remain there for additional tests. The 73-year-old former first lady was at a funeral for longtime Austin newscaster Paul Bolton when she fainted. Bolton, who had been hired by Lyndon Johnson in 1943, had worked with the young Walter Cronkite and Bill Moyers . . .

*An autopsy yesterday failed to establish a cause for the death of the 23-year-old son of entertainers Steve Lawrence and Eydie Gorme, who died Wednesday while being treated for an irregular heartbeat at UCLA Medical Center in Los Angeles. Michael Robert Lawrence was unconscious when he was brought into the hospital. He was an editorial assistant at Witt Thomas Productions Co. . . .

Loretta Cornelius, who was fired Wednesday as deputy director of the Office of Personnel Management, but who won't leave because she says she can only be fired by the president, is just holding to a long-stated conviction. She was interviewed by Lee Michael Katz in the January issue of Washington Woman about the pressure on her after her Senate testimony helped cost her boss, Donald J. Devine, his reappointment as director of OPM. Said Cornelius: "I serve at the pleasure of the president. If Ronald Reagan doesn't wish for me to serve, all he has to do is say so" . . .

First Lady Nancy Reagan has agreed to be honorary head of the nonprofit charitable trust fund set up by American Security Bank to aid the children of the astronauts killed in last week's space shuttle explosion. More than 5,000 contributions came in early this week for the children. Five of the seven space explorers had children . . .

The law firm of O'Connor and Hannan celebrated its 25th anniversary Wednesday, along with a wedding celebration for Patrick O'Connor, who recently married his one-time secretary of 20 years ago Evelyn Ledingham. A stellar crowd showed at the Sheraton Grand reception, including Sens. Lloyd Bentsen, Alfonse D'Amato, Alan Dixon, Paula Hawkins, Howard Metzenbaum and Claiborne Pell, former vice president Walter Mondale, former Washington Star editor Sid Epstein and former head of the Democratic National Committee Chuck Manatt . . .

The eighth annual Bartenders Ball kicks off tomorrow night at the Sheraton Washington Hotel with two regulars from the hit television series "Cheers" -- Kelsey Grammer, who plays Frazier Crane, and Woody Harrelson, who plays bartender Woody Boyd -- as the star celebrities. Other television celebrities there will include local talents Wes Sargenson, Mary Norton, Pat Collins and Yolanda Gaskins. Proceeds from the evening will benefit 15 local charities . . .