BOSTON -- Until last week, the blue Chevrolet Celebrity with license tag "STATE 1" that ferries Gov. Michael S. Dukakis (D) around on official business symbolized what his presidential campaign likes to call the "Massachusetts Miracle" of economic redevelopment.

Then on Wednesday, General Motors Corp. abruptly announced that, because of sluggish car sales, it is closing the Framingham, Mass., assembly plant where the governor's car was built and throwing 3,700 employes out of work.

The decision isn't likely to send the Massachusetts economy into a tailspin, but it was one of several small embarrassments to Dukakis who is trying to persuade voters nervous about the stock market and the weakened dollar that, as president, he would have the experience and the solutions to make the American economy healthy.

"Look, those are problems you have," Dukakis said of the GM decision, during a statehouse interview the day after it happened. "But we have a 2 1/2 percent unemployment rate and thousands of jobs going unfilled."

The next day, the federal government announced that the Massachusetts unemployment rate had jumped by 0.7 percentage points to 3.2 percent. That still left Massachusetts in the best shape of 11 large industrial states, but the one-month increase was the largest of any of those states.

Dukakis, who has been trying to get his campaign rolling after having accepted the resignations of his top two aides for their role in distributing a videotape that helped sink the presidential campaign of Sen. Joseph R. Biden Jr. (D-Del.), has pinned his presidential aspirations in large part on economic issues.

"What he did for Massachusetts, he can do for America," say his new television ads, which began running in Iowa on Thursday night.

But the question now is whether Dukakis has a credible message on the economy. His opponents, who have long questioned whether he can legitimately claim credit for the economic turnaround of his state, lately have begun to ridicule his proposal to shrink the federal deficit in part through more vigorous tax collection, something Rep. Richard A. Gephardt (D-Mo.) calls "hokum."

"I'm baffled," Dukakis said when asked about the criticism. "Any chief executive who comes into a situation where he's looking at a lot of red ink does two things. He looks at spending, and he looks at revenues. On the revenue side the first thing he does is determine whether or not he's got receivables and whether he can go out and collect them. And that's as true of someone in the private sector as it is in the public sector."

Dukakis claims $110 billion in federal taxes owed go uncollected and that the government could easily pick up $105 billion over five years and $35 billion annually thereafter. "That far exceeds anything anybody on Capitol Hill is talking about in terms of new taxes," he said. "Does that mean I rule out new taxes? No, and I've made that very clear."

But the tax collection proposal has drawn criticism in part because it sounds like a gimmick, a technical fix for a far more serious ailment. Already Dukakis is getting warnings that he needs to embolden his economic message.

New York Gov. Mario M. Cuomo (D) has sent Dukakis a not-so-subtle hint that he needs to broaden the scope of his economic platform.

Cuomo sent the message obliquely by raising the possiblity last week that he might endorse Sen. Paul Simon (D-Ill.). Prior to those comments most political insiders assumed that Cuomo had eyes only for Dukakis.

"There has been a degree of disenchantment with Mike," said one member of the Cuomo camp, who asked not to be identified, in explaining Cuomo's tilt to Simon. "I think there is a feeling on Cuomo's part . . . that running for president on the 'Miracle of Massachusetts' and improved tax collection alone is absurd."

Dukakis campaign officials, who defend the tax-collection plan as just one part of the governor's approach to the economy -- the other parts include spending cuts, especially in military programs, and an aggressive economic development strategy, lower interest rates and possibly new taxes -- say that Dukakis needs to do more.

Said Dukakis: "I think I'm probably more detailed when it comes to economic policy than any of the others out there {but} yeah, I will be adding and fleshing out."

Dukakis campaign officials say they are not concerned about Simon's rise in standing, even though he and Dukakis may be fighting over the same liberal voters in the Democratic caucuses and primaries. Their view is that Simon's rise only complicates things for Gephardt in Iowa and doesn't affect the outlook in New Hampshire, where Dukakis is heavily favored. They also say their fund-raising advantage -- they have raised $9 million -- means they can compete in many more places at once.

"We're not surprised where Simon is," said Paul Jensen, the Dukakis campaign's second-in-command. "We saw it developing three to four months ago . . . . Simon doesn't fundamentally change our perscription about Iowa, which is that Dukakis has to have a credible finish there. Either Gephardt or Simon has to win. Dukakis has to be close to the top."

Dukakis, who has been buffeted not only by the Biden tape episode but by legislative problems back home -- his ambitious plan for comprehensive health insurance almost was derailed in the legislature -- said he isn't spread too thin at a critical time in the campaign.

"When I went into {the campaign}, I knew one of my strengths is that I'm a sitting governor who is perceived by most people to have been a successful governor," he said. "On the other hand, that means I have to spend a good deal of time doing that job. When I made the decision to run, I accepted that . . . . Now that we're up and running, with good finances and organization, I'm going to pace things a little better."