Goalkeeper Valdes replaces Villarreal's Diego Lopez as Spain's third-choice behind number one and captain Iker Casillas of Real Madrid and number two Pepe Reina of Liverpool.
In the forward line, Pedro is included along with Bilbao's Fernando Llorente, while Fenerbahce's Daniel Guiza and Sevilla's Alvaro Negredo miss out. Martinez was preferred to Marcos Senna and Santi Cazorla, both of Villarreal.
"We assessed the players' form over the balance of the season and we need to take the best players regardless of age," Del Bosque said at a news conference.
The former Real Madrid coach also culled Atletico Madrid keeper David de Gea and Osasuna defender Cesar Azpilicueta from the preliminary 30-man squad he named earlier this month.
"We are guided by the head but the heart also helped," he added. "I know that missing out on a World Cup is a real blow."
The uncapped Valdes, Pedro and Martinez have all had excellent seasons for their clubs and although they are unlikely to get much time on the pitch in South Africa they are valuable additions to an exceptional group.
Pedro scored 23 times for Barca this season, netting often crucial goals in all six competitions the La Liga champions contested.
The 22-year-old from Santa Cruz de Tenerife bagged 12 in the league, four in the Champions League, three in the King's Cup, two at the Club World Cup, one in the European Super Cup and one in the Spanish Super Cup.
COMMANDING PRESENCE
His team-mate Valdes, 28, has long been overlooked by Spain coaches but won the Zamora award for the fewest league goals conceded for a second straight season as Barca let in only 24 in their 38 matches of the campaign.
He has ironed out the recklessness that marred his performances in the past and is a commanding presence in the penalty area and superb in one-on-one situations.
Martinez, 21, grabbed the headlines in April when he scored twice in a 4-1 win over Almeria, including a brilliant second where he left several defenders for dead with a weaving run.
"It's great news and I'll be with a team mate which is very positive for Athletic Bilbao," Martinez said on the club's website.
"I can't really explain what it means yet but of course I never expected the good fortune that I have had."
Among the European champions' injury concerns, Liverpool striker Fernando Torres and Arsenal captain Cesc Fabregas were in the squad as expected and Del Bosque said their prognosis was positive.
"We still have some slight concerns but they have been included because the message we are getting from the medical staff is positive and they are expected to arrive at the championships at 100 percent," he said.
Goalkeepers: Iker Casillas (Real Madrid), Pepe Reina (Liverpool), Victor Valdes (Barcelona).
Defenders: Raul Albiol (Real Madrid), Alvaro Arbeloa (Real Madrid), Joan Capdevila (Villarreal), Carlos Marchena (Valencia), Gerard Pique (Barcelona), C
