Democrat Michael Dukakis, bolstered by a new poll showing his lead widening in New York, campaigned on Long Island Friday with his rivals, pledging national health insurance and a safety-conscious Nuclear Regulatory Commission.

"If I am elected president, we're going to appoint people to the NRC who put the public, public health and public safety first," the Massachusetts governor told a forum at Adel-phi University, not far from the controversial Shoreham nuclear power plant.The NRC has expressed support for allowing Shoreham's owners to develop an emergency evacuation plan without state or local approval. Dukakis declared local and state governments must have "the authority to approve or disapprove an evacuation plan."

Dukakis, civil rights leader Jesse Jackson and Sen. Al Gore of Tennessee also told the audience of about 1,000 they would create a national health insurance program.

Jackson generated the most enthusiasm from the mostly white audience with his stinging criticisms of President Reagan for "$600 billion in tax relief granted to the affluent."

"Reagan has given the rich and powerful a $600 billion party, and he has invited those who don't attend this party to pay for the party," Jackson said.

Questioned about his lack of administrative experience, Jackson pointed to his suprisingly successful campaign for president.

"I've run the most cost-efficient, best-managed and least-funded campaign because I have been the most definite in leadership," he said.

The latest United Press International count of delegates either committed or projected showed Dukakis and Jackson running neck-and-neck for the nomination. In the count, Dukakis had 683.15 delegate votes with Jackson at 644.20. Gore was third with 386.55.

It will take 2,082 votes to win the nomination.

But Jackson faces an uphill battle for the state's 255 delegates, according to a Marist College Institute for Public Opinion poll released Friday.

If the April 19 New York primary were held today, the poll showed, Dukakis would win with 47 percent to Jackson's 30.5 percent. Gore was a distant third with only 6 percent.

Dukakis' lead was 10 points wider than it was last month, the telephone poll of 404 likely Democratic primary voters showed.

Jackson's New York campaign manager, Hulbert James, said, however, the poll did not reflect the deep commitment of Jackson supporters and said if turnout was high, Jackson would capture a much larger share than Marist predicted.

However, he added, "I am very concerned about what this poll is showing, and I hope it's not being used to manipulate the vote."

The Marist poll showed Dukakis is the preferred candidate of New York's Jewish community, which provides about a fourth of the primary vote. Dukakis had the backing of 69 percent of Jews surveyed, up from 59 percent in March.