FOLLOWING HIS recent detente with the Soviet Union, which he visited earlier this year, the distinguished British musician Elton John has consented to tour the United States. (He appears in Washington today for the first of two nights at the DAR's Constitution Hall.)

Since he is unabled to give interviews of more than three minutes' duration (apparently due to his need to conserve energy in order to achieve a state of boogie), an exclusive background briefing has been obtained from a senior official in Elton John's entourage.

This dignitary, Tony King, who is currently head of disco marketing for RCA records, has known Elton John even longer than Leonid Brezhnev has -- in fact, knew him even before he was Elton John, Indeed, as Elton John himself confided to this reporter -- in a remarkable two-minute dialogue in New York (which ended abruptly with Elton's abduction by an unidentified wimp thought by observers to be either a KGB agent or his manager) -- "Oh, you're talking to Tony? Don't believe a thing he says."

King's frank and candid assessment of the latest developments in the Elton John situation has been summarized below in a nine-point brief, which, according to intelligence analysts, is the most incisive, complete and up-to-date picture of Elton John's state of affairs now available anywhere in the West.

1) The Return to Global Influence: Elton had semi-retired about three years ago and quit touring, but has now unsemi-retired. King surmises he quit because he felt a bit stale and was fed up with the pressures of touring, particularly with a huge case. But then he started missing the applause, so he came back. "when he announced he wanted to retire, I think he seriously meant it that day," say King.

2) The Changing Image: Elton has traded in his trademark glitter eyeglasses for contacts, gotten hair transplants, junked the platform shoes and lost some weight, though he is still basically a short, chubby, pink, balding guy who waddles. He is playing smaller halls as a virtual one-man show (there's a drummer), very heavy on his old hits.

it is "a more sophisticated presentation," says King, who adamantly denies Elton is "going Vegas," as one New York critic groused. "You can't go on singing 'Crocodile Rock' for the rest of your life or else you end up becoming a parody of yourself. I think he wants to become a total entertainer rather than just be known as a flash-in-the-pan rock star of the '70s."

3) Elto-Soviet Relations: He liked Leningrad better than Moscow and drank lots of vodka and the people were great to him and the audiences were terrific and he felt the whole time that he was under surveillance and his room was being bugged.

4) Foreign and Domestic Affairs: The now historic Declaration of Bisexuality, says King, "if anything, improved the quality of his life because he was able to be much more relaxed about himself. He doesn't have to put on any phony front. It's no big shock if Elton is seen leaving a nightclub with a glamorous young boy rather than a glamorous young girl."

There was a big bit of apprehension about how the chaps in the soccer club would take it (Elton is a director of the Watford Hornets). But "none of them said a thing. It didn't faze them," King says. Also, the admission brought letters "from a lot of gay people who were sad because they had to hide their sexual preferences, because they lived in a small town or something like that, and they said how much he'd helped them. I think he knew then that he had done the right thing."

5) Economic Aid Cuts: Elton is now downplaying his fabled generosity, a good thing, asserts King, because his friends were taking advantage. Including King. "He used to call me up and say, "I'm making all this money -- let's go out and spend it.'" And they would. Fancy restaurants, Cartier's. And if King saw anything he wanted, it was his. All you had to do was drop a hint. "I mean, I have something like $12,000 worth of jewelry in the bank. In the end, I had to stop. I thought, no, that's not right." They had a little talk about spending, and Elton has since amended his policy: "Elton tends not to do that anymore."

6) Upholding Property Values: "He's so funny about little things. For instance, if I said to him that I needed anything, I'd get it. But try sipping his drink. He pulls such a face when I do sometimes. And yet if I said I wanted a glass of champagne, he'd but me a case of Dom Perignon.He's very quirky that way."

7) Alleged Jerry Brown Rebuff: King says Brown wanted to have dinner with Elton when the tour hit Los Angeles, but Elton said no: "He'd rather just spend the time with his own pals than rap with Gov. Brown. He's not going to relax and be himself. I'm sure the governor has an angle -- getting him to do a concert for nuclear disarmament or something. Though he has his opinions, Elton doesn't want to promote any cause."

8) Troubled Regions: A very emotional man, Elton: shy, very moody, easily hurt, but also capable of being obstinate.

"He used to be a mess," King says. "He's better at it now than he used to be. It used to be that if he met someone or fell in love or anything like that and got rejected or if his feelings got hurt, it would take him a long time to get over it." As a child, Elton led a sheltered, protected life. "It took him a long time to start experimenting with love and life. When I first met him 13 years ago, he was a terribly shy, awkward kind of person. He was given to looking at the ground when he talked to you until you got friendly with him. And then you realized that inside this funny little guy was a warm, amusing, intelligent personality. I think that this becoming Elton John, with all the flamboyant behavior, was a way of getting out of himself a little more."

King, who used to see himself as kind of a father figure (he's five years older), says that "now I feel he's taken off and he's his own person."

9) Systemic Collapse: Elton collapsed last year from nervous exhaustion while at home in England. In Los Angeles on this tourf, he collapsed in mid-concert. Flu, says King. "He over-does it. Whatever he does, he pushes himself to the limit. If he plays tennis, he runs for every single ball." There are no problems with drugs or alcohol, says Tony. "Elton can do anything and then stop." APPENDIX A: Biographical Data

JOHN, ELTON: Age 32 . . . height 5 feet-6 inches . . . weight variable . . . nearsighted . . . born Reg Dwight . . . grew up in middle-class suburbs of London, the only child of middle-class parents who wanted him to become a civil servant . . . began teaching himself piano at age 4 . . .

Attended Royal Academy of Music, studied classical . . . idolized Little Richard and Jerry Lee Lewis as a teenager . . . dropped out of high school . . . joined his first rock group at 14 . . . remained obscure singer-pianist-writer for years, unable to land record contract . . .

Began his rise in 1969 when he started writing songs with lyricist Ernie Taupin, whom he met through a help-wanted ad . . . changed name to Elton John when he cut his first record . . . in the early '70's was a dominant figure in rock music . . . has made at least 10 platinum (million-selling) albums . . . some years reported to earn $14 million . . . lives in mansion on large estate in Windsor near Queen's Elizabeth's castle . . . owns his own record company, Rocket Records, and an estimated 300 pairs of glasses, many of which glow in dark.