He also said Manchester United midfielder Paul Scholes, 35, had confirmed he did not want to play for England again despite media speculation he could come out of his seven-year international retirement.
In addition, Capello dampened the idea Everton's Spanish midfielder Mikel Arteta might play for England in the near future.
The Italian said he could have better handled the announcement he was bringing down the international curtain for 35-year-old Beckham after 115 appearances, a record for an England outfield player.
Capello revealed his decision in a television interview aired on the night England met Hungary in a friendly at Wembley on August 11 - before he had told Beckham himself.
"I regretted it immediately," the coach told a media briefing ahead of his team's opening Euro 2012 qualifiers against Bulgaria and Switzerland next month.
"(My assistant) Franco (Baldini) spoke to him two hours after the interview and then I spoke directly with David on the telephone and I explained what really happened.
"Our relationship is really good. I spoke with David because he was part of the staff at the World Cup in June. I usually don't speak on the phone with the players, in my career I have never done this."
Capello said he was convinced he was right to end Beckham's England career and stuck by his decision to focus on younger players ahead of Euro 2012.
"I think the future is for the young players. The door is always open for all the players but now I am thinking about the younger ones who need to play more games to get more experience," said the Italian.
Beckham, who has had spells with Real Madrid and AC Milan, has spurned Capello's invitation to play one more "farewell game" in the friendly against France at Wembley in November and has also said he has no intention of becoming a manager once his playing days are over.
DIFFERENT STYLES
However, the England coach thinks the Los Angeles Galaxy midfielder would be good in the role.
"He has a lot of experience. He knows different styles of play in Spain, Italy and United States and has learnt a lot of different things," said Capello. "I think he can be a good manager, it's a difficult job but he is intelligent."
Capello also said Beckham's former United team-mate Scholes had told him he was too old to play for England again.
The coach considered Scholes for his World Cup squad but the midfielder turned him down.
Capello said Baldini talked to Scholes again last Wednesday, explaining: "We spoke to him and he said he felt he is too old to play for United in the Premier League and the Champions League - and the international team."
The coach added he would not entertain calling up Arteta who could qualify to play for England under FIFA's eligibility rules having lived in the country for more than five years.
"I like to think about the players I can select," said Capello. "When we ca
