
At the 58th FIFA Congress, 155 associations voted in favour, five against and 40 abstained.
The vote empowered Blatter and UEFA head Michel Platini to explore "all possible means within the limits of the law to ensure that these crucial sporting objectives are achieved."
Blatter said: "The FIFA president is asked, together with the UEFA president (Platini) to explore - and explore is not to discuss, explore is to go in depth - within the limits of the law.
"Anyway, the application of such a system would start only at the end of 2010 and we would start progressively with four, five and six (players)."
Football Federation Australia head Frank Lowy backed the resolution.
"We have a problem that we are losing lots of players," Lowy told delegates from the 201 countries represented. "These young boys between 18 and 20 go to these countries, get nowhere, get disappointed and they lose football."
FIFA faces a stiff challenge in having the rule approved by the European Union (EU), which in 1995 issued the landmark Bosman ruling that forced an end to all foreign-player restrictions.
The 27-member EU, through Employment Commissioner Vladimir Spidla, pre-empted the 6+5 plan by handing it a red card.
"If any country allows its soccer associations or leagues (to obey the rule) they will be in violation of EU rules, which oblige the commission to apply infringement proceedings," Spidla was reported as saying in Brussels earlier this week.
Blatter, who was scheduled to meet with European Parliament President Hans-Gert Poettering on June 5 in Brussels to discuss the issue, signaled he was ready for a fight.
"Speaking about it is illegal. For whom? And when? And if it is a law, you know, law can be amended, altered," the Swiss national said.
Blatter said he would appeal to the EU to accept the 6+5 rule under the rubric of the EU's own "specificity of sport" principle.
"We are only asking for a bit of solidarity," he said. "I'm sure it will be done."
English Football Association chief Brian Barwick was less than enthusiastic about 6+5, telling Australia's AAP news agency that "we're still great believers in the meritocracy that players should be in the team on performance and on ability first and foremost."
Barwick noted pointedly that Manchester United, one of the world's richest clubs, had won this year's Champions League final with six homegrown players in its starting side.
England's Premier League will be most affected by the 6+5 rule because it has the money to buy up talent globally.
Blatter announced changes to the rules covering the eligibility of players to represent national sides. He poured scorn on Qatar for the ease with which Brazilian-born players could get citizenship.
DPA