Health officials in New York, California and other hard-hit parts of the country are restricting coronavirus testing to health care workers and the severely ill, saying the battle to contain the virus is lost and the country is moving into a new phase of the pandemic response. As cases spike sharply in those places, they are bracing for an onslaught and directing scarce resources where they are needed most to save people’s lives. Instead of encouraging broad testing of the public, they’re focused on conserving masks, ventilators and intensive care beds — and on getting still-limited tests to health-care workers and the most vulnerable. The shift is further evidence that rising levels of infection and illness have begun to overwhelm the health care system.