WASHINGTON — The easiest way to gain entry into the United States is not to walk across the border in the dead of night. It is to write a check.

A visa process enacted by Congress in 1990 to create jobs and pump billions of dollars into the economy has evolved into a program that federal investigators and some prominent lawmakers say has become a risk to national security and an easy mark for abuse, particularly from China.

The program, called EB-5, allows wealthy foreign investors, for a price ranging from $500,000 to more than $1 million, to put themselves on a path to United States citizenship. The money must be used to finance a business in this country and eventually employ — directly or indirectly — at least 10 American workers in economically depressed areas.

But EB-5 has been the subject of increasing scrutiny since investigators uncovered numerous cases of fraud, discovered individuals with possible ties to Chinese and Iranian intelligence using fake documents and learned that international fugitives who have laundered money had infiltrated the program.