In America, where celebrities are as interchangeable as light bulbs, it surprises no one that actor Albert Finney has done an album of songs.

In Britain it's another story. People don't know quite what to make of it - even though this kind of thing has been happening for years: Rex Harrison in "My Fair Lady," Richard Burton in "Camelot," Richard Harris with his hit single, "McArthur Park."

Albert Finney? they say. The man who brought Tom Jones and Hercule Poirot to life on film? The man who did "Luther" and "Saturday Night and Sunday Morning" and Tamburlaine and Hamlet and "Joe Egg" and "A Flea in Her Ear?" The man Time called "the most brilliant actor of his age in the English-speaking world?"

The British, as Finney put it during a brief visit to Washington, do like to pigeonhole their stars, and it confuses them when one steps out of character. This may be, in fact, a reason why Finney has ranged so far in his roles.

The range has extended even farther with release of "Albert Finney's Album" by Motown.

"It just happened," Finney said. "In 1960 I did a stage musical, 'The Lily-White Boys,' but that was the only musical except for the film 'Scrooge.' Well, at the time I got a letter from a music publisher suggesting I do something more, I never gave it another thought."

Then, 15 years later, the actor was talking with his friend Denis King, a composer-conductor, about getting some organ music for a film he was directing. The two of them drifted up-stairs to chat with a King crony - who turned out to be the music publisher.

"He said why not try some songs. I said all right, and I did a demonstration tape with six standard tune. The publisher liked it. But I had a funny feeling about it, I don't know what, I thought perhaps I could try some lyrics of my own."

So he wrote a couple of songs, showed them to King. They were a natural. King found that melodies sprang from them with almost none of the usual jimmying and tinkering.Meanwhile, Finney was waiting for the new National Theater to open: He was to star in the marathon Marlowe epic "Tamburlaine" to launch the theater, and construction delays had set opening night back three months.

"I had time on my hands," he said. "I did six more songs. Then it occured to me we might try an album. We had the $20,000 it would cost, and I wrote four more songs, and we did it. Then Motown picked it up." He still seemed slightly astonished at the whole thing.

The songs are about his feelings, his encounters with life.

"What have they done to my hometown?" one begins.

"They've pulled the terraced houses down

"And put the people in the sky

"In towers 20 stories high -

"It's very hard now to relate

"To meet with folk, communicate . . ."

His hometown is Salford, close to Manchester, and his complaint about high-rises will echoed by Britons from London to Newcastle.

The curious thing is that, in his 41 years, Finney has not been a writer at all. He'd never written a thing. When he got an honorary doctorate of letters from Sussex University, he phoned his father to tell him the good Sussex University, father said, "Doctor of letters, eh? You never even send me a postcard."

The lyrics come quickly, and he especially enjoys hearing them set to Denis King's music, which adds a new dimension. He plans to do another album if this one goes over. But nobody should think for a moment that Albert Finney is lost to the stage.

"I have an arrangements with the National Theater," he said. "I work there 16 months and then take eight off for films or other projects. We've commissioned a script for a film, but we didn't like the first version. There's very little money in England for cinema these days, except the Carry-On comedies and the Confessions series (as in 'confenssions of a Window-Cleaner'); it's all gone into television.

Films are fun, he added, but there is nothing like acting on the stage, building emotional intensity through an evening and with luck taking the audience with you, using yourself up in the kind of sustained experience that is impossible in film work.

"I'll be playing Macbeth in the fall." he said "I'm still not sure what I'm doing here in Washington promoting these songs . . . ."