In eighteen months she travelled from a schoolgirI's life in a South Wales Valley, to the offices of the Beatles, to the top of the charts, to Buenos Aires, to America, to the London Palladium and to dinner with Prime Minister Harold Wilson at No. 10 Downing Street.

It was a rugged yearand-half for Pontardawe's beautiful blond MARY HOPKIN Britain's representative in the Eurovision Song Contest but Mary smiled and sang and came through the experience as quiet and as diffident as before. She now follows the Beatles and the Plastic Ono Band as the biggest-selling international name on the Apple label.

Today, in 1970, there must be few people in the western pop music world - and outside it - not familiar with the dreams-come-true story of MARY HOPKIN'S swift rise to world stardom.

One day she was no morethan a shy 17 year old schoolgirl nervously trying for success in television's ''Opportunity Knocks" TV talent contest.

The next she had been noticed by Twiggy and mentioned to Paul McCartney.
And the next she was recording ''Those Were The DayS" and watching it soar to No. 1 in Britain and just about Here, There and Everywhere. It sold more than four million copies.

''Those Were The Days" was released in the autumn of 1968 and became one of the biggest records of the year - a magnificent anthem to nostalgia that was broadcast over and over and over agaIn.

Throughout that winter, Mary and McCartney worked on a follow-up album, ''Postcard", recording pretty songs to complement the soft purity of her voice. This was released in the February in 1969.

A few weeks later followed Mary's second single for the Apple label, a composition by Paul called ''Goodbye''. lt was an instant hit and by an apparent twis of fate only the continued success of the Beatles'''Get Back" stopped her making No. 1 again. She made number two.

Almost a year passed between the release of "Goodbye" single and Mary's latest single withApple, ''Temma Harbour," but it was a year that was far from idle.

ln those rocketing twelve months. Mary appeared in the Tom Jones series networked across America, Britain and elsewhere; sang at Midem '69; starred in a nationwide concert tour with Engelbert Humperdinck; appeared in Canada and in cabaret in New York; toured Brazil, Chile and the Argentine; returned to America again and again; dined with the Prime Minister; and topped the bill with Tommy Steele in pantomime at the London Palladium.

Talk to Mary and she may not tell you about these world adventures and her pride in achieving so much in so little time.

She isn't being blase... the fact is that to MARY HOPKIN, conversation about her travels or any of the trimmings of showbusiness hardly matters at aIl. ''1 I just want to sing." she repeats with whispered determination. ''l just want to sing."

She admits to having hardened up a little since her beginnings in the world of pop music, but only a little, and only inside. ''AII it is," says Mary. ''is that l've grown up."

''l used to feel that many people in showbusiness were insincere; no l've met some marvellous people and I realise that it takes all kinds to make the world.

''lf there's one thing that hasn't changed in me, it's being sensitive to newspaper critics.

''Maybe it's that because I always want perfection in whatever I do, and l worry too much. I don't mind if criticism is constructive, because that's a help. But I do always try to be of my best, anyway l want to be a good singer. I want to be liked and I know l've got a lot to learn.

Suddenly the door opens and Mary has two visitors - children from Wales - and for a few minutes she talks with them -in her native Welsh. Autographs are signed and she glows visibly as they say goodbye with warm smiles on freckled faces.

"I don't think I could settle in London, even though so much of my life is now there. l need Wales and my home and my family too much to be away for long.

"My future? Well, l'd like to dance more. I'd like to try films. l'd like to try and remain more of a folk singer than a pop shger. lId like to buy a quiet cottage in the country. l'd like to know about classical composers and their music - and l'd also like to write a song myself.

"Most of aIl. I just want to be better. l love singing and it's my life, but sometimes I get frustrated because I think that singing is the limit of my talent.

"I want to do so many things. and do them well. I believe in trying."