AUGUSTA – Gov. John Baldacci on Wednesday updated a re-election campaign claim that his economic plan is working by citing new Census Bureau data that, to the initial puzzlement of economic analysts within and outside his administration, showed Maine’s median household income growing by 5.5 percent from 2004 to 2005.

“The U.S. Census numbers show that many people in Maine are finding opportunities to work and increase their earnings,” Baldacci said.

On Tuesday, as the Census Bureau released its findings, several Baldacci administtration figures said they were taken by surprise.

State Economist Catherine Reilly said the reported jump in median household income presented “a different picture than we’ve seen from other data.”

Another expert, Professor Charles Colgan of the Muskie School of Public Service at the University of Southern Maine who serves as chairman of the Consensus Economic Forecasting Commission, said at first blush he would question “that big a change in that short a time period.”

Calling the growth finding “unusual,” Colgan added, “it’s not what you would expect given overall growth in the economy for that period.”

Not long ago, a report by the Federal Reserve Bank of Boston found that “New England’s northernmost state did little but tread water in 2005, as 2004’s mild growth came to a standstill.”

It cited “lackluster” employment measures, “tepid” income growth, a cooling housing sector and a decline in the value of merchandise exports.

“Maine’s recovery seems to have stalled,” the report said, adding that, “In fact, Maine was the only state in the country to see a decline over this period, except for Louisiana.”

Ed Welniak, chief of the income surveys branch of the Census Bureau, said Wednesday the new report’s findings put Maine among seven states showing an increase, and that statistically none of the state increases could be said to be larger than another.

Baldacci said Wednesday his economic plan includes “investing in higher education, expanding research and development; expanding the reach of investments and incentives; enhancing renewable and alternative energy sources; and continuing tax relief efforts.”

Later on Wednesday, the Republican Governors Association announced it had begun running issue ads in Maine outlining GOP gubernatorial candidate Chandler Woodcock’s experience and headlining his policy agenda.

The ad credited Woodcock with seeking lower taxes and government spending curbs.

“Tell Chandler Woodcock you support new solutions to change Maine’s direction,” the ad script says.

In a statement announcing the airing of the ad, Massachusetts Gov. Mitt Romney, the chairman of the Republican Governors Association, said: “Under the current administration, Maine is experiencing out of control state spending and an unhealthy tax burden.”

It was unclear Wednesday whether the ads would trigger additional disbursements of public campaign funds to the other two gubernatorial candidates who qualified for Clean Election state funds, independent Barbara Merrill and Green Independent Pat LaMarche.

A decision will be based on whether the ad includes “expressed advocacy,” said Jonathan Wayne, executive director of the Commission on Governmental Ethics and Election Practices. If the ad is found to directly advocate for a candidate’s election or defeat, additional disbursements to Merrill and LaMarche could be authorized, Wayne said.

The matter has been brought to the attention of the ethics commission, whose staff will take it up and decide if the ad clearly includes expressed advocacy. If the answer is not so obvious, it might be referred to the agency’s commissioners, Wayne said.

The issue ad also could give Democratic candidate Baldacci the go-ahead to spend more money to counter the pro-Woodcock piece without triggering matching funds to the Clean Election candidates, Wayne said.