Vice President Mondale today hit the Labor Day picnic circuit in two crucial industrial states, Pennsylvania and Ohio, picking up endorsements from prodigal Democrats and defending the Carter administration's economic record.

Mondale was welcomed to Cleveland by Sen. Howard Metzenbaum, Rep. Louis Stokes and Cuyahoga County Chairman Tim Hagan, all of whom backed Sen. Edward Kennedy against President Carter.

Stokes gave Mondale a rousing endorsement at an outdoor picnic, telling the crowd, "In the primary you can play around. You can send a message to someone . . . now it's time for serious business."

"This Democratic Party is unified again," Mondale said. Carter lost Cleveland to Kennedy, but carried Ohio in the Democratic primary.

Earlier, Mondale picked up support from Senate candidate Pete Flaherty, another former Kennedy supporter, and told about 1,000 people at a picnic in Westmoreland County in western Pennsylvania that the Carter administration created eight million new jobs.

Carter carried western Pennsylvania against Kennedy, but lost the state to his Democratic rival.

Unemployment is at 9 percent in the four-county region of western Pennsylvania where Mondale was the guest of honor at an outing organized by a group of labor unions.

Mondale repeatedly cited the endorsements the Democrats have received from labor unions as evidence that organized labor's rank and file wil stay with the Democrats in November despite high inflation and unemployment.

Mondale also said the new Carter economic program should have special appeal to the older industrial states like Pennsylvania and Ohio where decaying factories are in need of new capital investment.

Mondale referred to the Polish workers' strike and brought cheers from the crowd by declaring: "The news from Poland this Labor Day is welcomed by all Americans."

Instead of attacking Republican candidate Ronald Reagan, Mondale invoked the Democratic Party traditions of his mentor Hubert H. Humphrey and of Harry Truman. He also recited Carter administration achievements in social and economic policy areas.

In his only reference to Reagan, Mondale told the labor picnic that at election time the Republican Party "starts to sound like Democrats."

Reagan, he later told reporters, has taken "a classically anti-labor position."