FINA has come under criticism for its failure to regulate the rapid advances in swimsuit technology that have led to 108 world records last year and nearly 30 so far this year.
Some suits are suspected of creating "air trapping" effects that enhance speed.
A U.S. proposal to limit the amount of swimsuit coverage - between the waist and knees for males, not beyond the shoulders or below the knees for females - was overwhelmingly passed by the FINA congress, meeting in Rome during the world championships.
The new rule also says suits shall only be made from "textiles," but that term has yet to be defined.
"The most important thing is that it's textile only," Mark Schubert, head coach and general manager of the U.S. national team, told The Associated Press. "I think we sent a strong message as to our feeling of what the suit should be."
The new rules won't take effect at these swimming championships, where dozens of world records could be set in suits made from materials such as polyurethane.
The legislation was passed as a general rule, but then a subsequent motion from Britain to make the rules part of FINA's bylaws was accepted, putting the matter in the hands of FINA's bureau.
General swimming rules only come up for discussion at the FINA congress every four years, whereas the bureau meets several times each year, and can also convene on short notice.
"We didn't disagree with the U.S. proposal, but we wanted the flexibility to amend it as technology moves on, and we can now," said David Sparkes, the chief executive of British Swimming. "Technically, the bureau could even convene over e-mail.
"For sure it's not the end of the road in terms of innovation."
But bureau bylaws pertain only to world championships and Olympics.
"FINA rules in general are only for worlds and Olympics. It's normally up to each federation to decide on their own rules," FINA executive director Cornel Marculescu said. "We will clarify it and hopefully finish with the suit controversy."
USA Swimming will conform to the international standard.
"Our policy has always been to follow FINA rules," Schubert said.
The question of how to define textiles is unlikely to be determined until the next FINA bureau meeting in September or October.
With the high-tech bodysuits still in use, multiple records are expected in this meet - records that could stand for some time.
"I think it will be difficult to eclipse those records if we go back to true swimming, without the rubberized suits," Schubert said. "The East German times (achieved by athletes using performance enhancing drugs) stood for a long time, but even they got broken, so I'm sure our athletes will be up to the challenge."
Schubert also backs attaching an asterisk to records set over the last 18 months.
"That's something the FINA bureau is going to have to address. That was just an idea, perhaps to have two lists - one list with the new suits, then one list with the old suits," he said.
The Americans originally wanted men's suits to be limited only from going beyond the shoulders or knees.
"We amended it last night after meeting last night with Cornel and the coaches of the major swimming countries, and that was the consensus of the coverage that they wanted, so that's why we made the switch," Schubert said.
"It was a little bit more severe switch, but we're pleased."