The world was looking to the US, Mr Obama said, but added that the outbreak required a "global response".
The measures announced included ordering 3,000 US troops to the region and building new healthcare facilities.
Ebola has killed 2,461 people this year, about half of those infected, the World Health Organization (WHO) said.
The announcement came as UN officials called the outbreak a health crisis "unparalleled in modern times".
The WHO says the most urgent immediate need is more medical staffThe funds needed to fight the outbreak have increased 10-fold in the past month and $1bn (£614m) was needed to fight the outbreak, the UN's Ebola co-ordinator said.
'Massive surge needed'Mr Obama said that among other measures, the US would:
- Build 17 healthcare facilities, each with 100 beds and isolation spaces, in Liberia
- Train as many as 500 health care workers a week
- Develop an air bridge to get supplies into affected countries faster
- Provide home health care kits to hundreds of thousands of households, including 50,000 that the US Agency for International Development (USAID) will deliver to Liberia this week.
Tulip Mazumdar, global health correspondentMr Obama announced the sort of help that the WHO, Medecins Sans Frontieres and others have been calling for for many weeks.
Cumulative deaths - up to 13 September