BOSTON — Boston Marathon organizers announced changes to their registration system Wednesday to ensure the fastest runners have spots at the starting line.

The move by the Boston Athletic Association comes after this year’s field filled up in just eight hours, frustrating qualified runners who were left out.

Starting with the 2012 marathon, the association will begin a two-week online registration period that gives those with the best times multiple chances to apply before the process opens to slower runners.

And to reduce the pool of runners in the future, the BAA will lower qualifying times in each age group by five minutes, beginning with the 2013 race.

The association’s executive director, Tom Grilk, said the changes have two basic goals: rewarding excellence and increasing fairness to avoid repeating “one of the most troubling days we’ve ever had.”

Grilk said the association heard from a flood of intensely disappointed runners who’d put in the grueling work to qualify this year.

“For us to tell people who have done that that there was no room for them was a very bitter pill for us,” he said. “Not as bitter as it was for them, but bitter nonetheless.”

Runner Anthony Anscombe, 50, admits he’ll “always be ticked” he was shut out this year of what would have been his third Boston Marathon, a race he’s truly enjoyed. He added, “I’m just not going to sweat it going forward.

“They’ll probably have really good races, and they’ll have really hardcore people,” said Anscombe, a Chicago attorney. “But for people who I guess who would describe themselves like me as a recreational marathon runner, I think it’s going to be very hard to run it anymore.”