FLINT, Mich. — Michigan’s attorney general opened an investigation Friday into lead contamination in Flint’s drinking water, and the governor asked President Obama to declare a disaster as National Guard troops fanned out across this anxious city to help distribute bottled water, water filters and testing kits.

The actions drew new scrutiny to an environmental crisis that poisoned the water supply for a year and a half before it was addressed. The contamination has left a city of 100,000 people unable to use tap water for drinking, cooking or bathing, and has caused mounting political woes for the governor, Rick Snyder.

In the last three weeks, a panel appointed by Mr. Snyder reported that state officials had for months wrongly brushed aside complaints about the contamination. The governor apologized for the state’s performance, Michigan’s top environmental regulator resigned, and federal agencies announced that they were investigating.

In recent days, even as Mr. Snyder has declared a state of emergency, requested federal action and summoned the National Guard, he has continued to face intense criticism that the state has been slow to react, despite admitting that it bungled the problem.

In Flint, a poor city plagued by aging infrastructure and declining population, residents and business owners voiced anger, frustration and fear.

“I mean, this is insane, you know?” Sonya Houston, 42, said as she visited a fire station to pick up a water filtration pitcher. She said that she and her husband had only recently found a new home and that their daughters, ages 7 and 8, “can’t even use the water in their own home.”

Now, they are considering moving out of the city. Holding up the pitcher, she said, “This is not enough to keep us here.”

Jason White, vice president for medical affairs at a local hospital, McLaren Flint, said the water supply became so poor in 2014 “that we got reports from our sterile processing people, those who clean the surgical instruments, that they were seeing corrosion,” prompting the hospital to replace its water filters.

Since Monday, when officials began distributing emergency supplies at fire stations, thousands of people have streamed in, and aid workers have rationed lead testing kits, one per person, for fear of running out. “The volume of people that have been coming here, it’s a nonstop deal for 12 hours a day,” said David Cox Jr., the city fire chief. “We weren’t ready for it.”

The governor sent two requests Thursday night to the Federal Emergency Management Agency, which this week has been distributing its own surplus supplies of bottled water, saying that the crisis was beyond the state’s ability to manage. One asks that the president declare a state of emergency, allowing for immediate assistance like water, food and generators; the other asks him to declare a major disaster, allowing for millions of dollars in loans and grants to residents and the state for long-term needs like new water pipes, an improved filtration plant or temporary housing for residents.

FEMA and the White House declined to offer a timetable for a decision. But Representative Dan Kildee, a Democrat whose district includes Flint, said, “We expect something within the next couple of days.”

The attorney general, Bill Schuette, said Friday that his office would investigate “what, if any, Michigan laws were violated in the process that resulted in the contamination crisis.” Mr. Schuette, a Republican, is considered a likely candidate for governor. Mr. Snyder, also a Republican, cannot run again in 2018 because of term limits.

The Environmental Protection Agency and Department of Justice are also investigating possible violations of federal law.

Neither those agencies nor the office of Mr. Schuette (pronounced SHOO-tee) would say what people or agencies might be the subjects of the investigation. But the recent report from a task force appointed by the governor blamed the state’s Department of Environmental Quality, saying that officials there had taken a lax approach to enforcement and that they responded to concerns about Flint’s water with “aggressive dismissal, belittlement and attempts to discredit these efforts and the individuals involved.”