The decision in the long-running dispute was a victory for Obama, removing one of the last stumbling blocks on his march to the nomination and preventing Clinton from significantly cutting his lead in the hard-fought race.
Only three contests with 86 pledged delegates at stake remain -- Sunday in Puerto Rico and Tuesday in Montana and South Dakota -- and Obama is about 70 delegates short of the 2,118 now needed to clinch the nomination.
That means he will likely still be short of the total on Tuesday, but could reach it quickly with the help of some of the approximately 180 superdelegates -- party officials who can back any candidate -- who remain uncommitted.
"Now that Michigan and Florida have been added, we are getting close to the number that will give us the nomination," Obama said in South Dakota after the rules committee meeting.
"And if we've hit that number on Tuesday night we will announce that, and I think even if we don't, this is the end of the primary season." Voting ends in Puerto Rico on Sunday at 3 p.m. EDT (1900 GMT) with results expected shortly afterward. The territory, where Clinton is favored, has 55 delegates at stake.
Obama will hold a victory celebration after the South Dakota and Montana polls close on Tuesday night at the Xcel Energy Center in St. Paul, Minnesota -- the site of the Republican convention in September.
The shift to the November presidential race against Republican John McCain came after the party ended a lengthy furor over the disputed results in Michigan and Florida.
Those contests, both won by Clinton, were not sanctioned by the party after a dispute over their timing and both states were stripped of their delegates.
All candidates including Clinton had agreed not to campaign for the contests, and Obama was not on the ballot in Michigan.
But once Clinton won she had pushed for the delegations to be seated at full strength, hoping it would boost her popular vote total, cut into Obama's delegate lead and strengthen her argument to superdelegates that she would be the stronger candidate in November.
Clinton's campaign responded angrily to the panel's decisions. Campaign aides said they could appeal to the party's credentials committee and carry the fight to the convention in Denver.
"Denver, Denver!" chanted Clinton supporters after the vote. Many Clinton backers shouted angrily at the panel as it tried to conclude the votes, making it hard to continue.