The conference's member presidents, meeting in Philadelphia, voted unanimously Tuesday to extend invitations to football-only and all-sports members. Commissioner John Marinatto declined to name the schools being targeted.
He did say he expected the targeted schools to accept, but added that there are still details to work out with each institution.
"As we've learned over the last two months, don't believe anything anybody tells you. Nothing's done until it is over," Marinatto said. "So I'm obviously being very cautious and that's why I'm reluctant to say names of schools."
He did acknowledge the league intends to expand west.
On Thursday, the Idaho State Board of Education will hold an "athletic conference discussion" concerning Boise State, The Idaho Statesman reported Tuesday. Boise State would require the board's approval to change conferences.
Boise State and Air Force of the Mountain West and Navy, a football independent, have been widely reported as the Big East's football-only targets, along with Houston, UCF and SMU of Conference USA for all sports.
"We have not received an invitation from the Big East. However, we understand that things are moving in that direction," UCF spokesman Grant Heston told ESPN's Joe Schad on Tuesday.
Navy athletic director Chet Gladchuk said Tuesday he had not yet heard from any Big East officials.
The Big East has been strategizing ways to divide its football teams into east and west divisions for football, with Temple, Memphis and BYU all considered as possible seventh additions, sources told ESPN's Joe Schad.
A source with knowledge of the Big East's decision told AP that Temple and Memphis are being considered. Memphis athletic director R.C. Johnson said the school has not had contact with the Big East but is holding out hope that it will as the expansion process continues to unfold.
Temple athletic director Bill Bradshaw declined comment. A BYU official declined to comment when asked if the Cougars had been approached by the Big East.
Boise State and Air Force, both in the Mountain West Conference, and Conference USA members SMU and Houston would be in the Big East's western division, along with Louisville and Cincinnati, a source told the AP. Navy, an independent, and UCF, also from C-USA, would be part of the league's eastern division with Connecticut, South Florida, Rutgers and another school. The league would then likely play a conference championship game.
The Big East believes UCF, Houston and SMU will be the first three schools to accept an invitation for 2013, with that process officially concluding within a week, a source told Schad.
The Big East also believes it was warmly received by Boise State. But of the six schools in the next phase of the conference's expansion plan, the Broncos' addition is the most challenging, sources told Schad.
Boise State is seeking confidence that it will be joining a conference that is very likely to maintain its automatic qualifying status for the Bowl Championship Series, sources told Schad. The Broncos also would like a western partner in the expanded Big East -- either Air Force, or if that's impossible, perhaps BYU.
"We're having discussions with Big East officials and continue to consider all of our options," Boise State spokesman Frank Zang said.
A Mountain West source told ESPN.com's Andy Katz that Air Force indicated to at least one conference president last week that it didn't want to leave for the Big East. Another MWC source said the Falcons have been reluctant to depart. But two scenarios are keeping the options open for the Falcons -- the promise of a $10 million payout from a possible television deal and if Navy decides to commit.
The WAC, WCC and Big West commissioners all told ESPN.com on Tuesday afternoon that they haven't heard from the Falcons or Boise State about membership for its other sports.
Meanwhile, a conference commissioner source said that there is serious panic within the MWC and C-USA about possibly losing key members of both leagues to the Big East. C-USA could survive losing Houston, SMU and UCF to the Big East since it would be down to nine schools. But if the MWC were to lose Boise State and Air Force, then it would be down to eight members in football (seven in all sports) and likely would pounce on the WAC's Utah State and San Jose State to replace those two schools.
Marinatto has had in-person meetings with officials at Boise State, Air Force and UCF.
Big East members Pitt and Syracuse are headed to the ACC, while TCU and West Virginia are bound for the Big 12, putting the Big East in a serious bind.
"The addition of these members will extend our reach, bring us to exciting new markets, strengthen our status within the BCS, and lay the foundation for possible further expansion, all while maintaining the high quality and standards our conference is known for," Marinatto said in a statement.
Marinatto also said that the Big East's presidents are committed to enforcing the league's 27-month waiting period before any departing school can leave. West Virginia filed a lawsuit against the Big East on Monday, arguing it should be allowed to leave for the 2012 season because the league breached its contract.
"The conference believes these claims to be wholly without merit and will explore all its legal options to protect its interests and to ensure that West Virginia lives up to its obligations," Marinatto said.
The ACC has said it will not challenge the Big East's rules, but the Big 12 needs 10 teams to fulfill its television contracts in 2012 and has said it expects West Virginia to replace Missouri and join the league next year. Missouri is expected to leave for the Southeastern Conference soon.
West Virginia filed a lawsuit Monday challenging the Big East's waiting period and asking the court to speed the school's divorce from the league.
"I quite frankly was stunned when I heard the news that they were filing a lawsuit," Marinatto said. "I couldn't understand under what grounds."