The WFP said shortages of rice in the communist run country's south and centre stem from a combination of weather factors last year dry spells, a late rainy season and flash floods.
"We're now raising funds" to support an emergency rice distribution probably in June or July, filling a gap before the harvest which occurs around November, WFP spokeswoman Cornelia Patz told AFP.
In the meantime, villagers will have to use stocks from the last harvest or buy rice in the market but prices are now "very, very high compared to last year", she said.
A joint study by the WFP and the UN's Food and Agriculture Organization (FAO) said weather shocks "impacted already vulnerable households" in areas that had not fully recovered from Tropical Storm Ketsana.
Ketsana struck in October 2009 and led to some of the worst flooding in Laotian history. It killed at least 11 people, caused more than $100 million damage, and prompted a government appeal for international help.
While starvation is not now a major concern, coping with limited food resources can have knock-on problems such as a reduction in protein, which can lower resistance to disease, Patz added.
Rice is the staple food in Laos and per capita consumption is among the highest in the world, the WFP-FAO study said.
Laos has about six million people and is one of Asia's poorest nations.