By Patricia Zengerle

WASHINGTON (Reuters) - Honduras President Juan Hernandez wants the United States to invest billions of dollars to help curb the flow of illegal migrants from Central America, and said it will take much longer to stem the crisis without Washington's help.

"If we have to do it alone, it will take us more time. But if we can do it together, it can be quicker and better for everyone," he told Reuters in an interview on Wednesday.

Hernandez was in Washington for an InterAmerican Development Bank meeting with his counterparts from Guatemala and El Salvador as well as U.S. Vice President Joe Biden on ways to overcome violence and poverty largely fueling the exodus from their countries.

The arrival of tens of thousands of illegal migrants from the three countries - including more than 60,000 children traveling without parents - caused widespread alarm in the United States, and a political problem for President Barack Obama as he pushed for sweeping immigration reforms.

Struggling to stop the flow, Honduras, Guatemala and El Salvador presented U.S. officials with an ambitious development plan in September to improve their economies through infrastructure investments.

Guatemala has said it is seeking $10 billion - some $2 billion a year for five years - toward the effort, chiefly from the United States.

Honduras would like that much or more, Hernandez said.

"It could be ($2 billion a year), it could be a little more," he told Reuters, speaking in Spanish. But U.S. officials have not said how much they will invest, he added.

Hernandez also said the migration crisis is a humanitarian issue, and Washington shares responsibility because of U.S. demand for drugs trafficked through Central America.

He argued that investing to improve the Honduran economy made more sense than spending huge amounts on a futile effort to seal the land border with Mexico.

Hernandez will promote the investment plan to Democratic and Republican lawmakers this week, but it could be a tough sell. Immigration is a hot-button issue in the U.S. Congress, where many Republicans insist Washington should focus mainly on excluding undocumented newcomers.

Lawmakers have approved only a fraction of the $3.7 billion for the border crisis Obama asked for in July.

(Additional reporting by Melinda Ulloa; Editing by Dave Graham and G Crosse)