Democratic Party leaders, increasingly optimistic about the off-year election outlook, previewed a new policy statement this weekend that borrows President Reagan's 1980 themes and gives them a reverse partisan twist.

The party's executive committee and state chairmen heard former Utah governor Scott M. Matheson, the head of the national Democratic Policy Commission, say that its July manifesto will emphasize "protection of families, jobs, independence, opportunity, freedom and national security."

The list is almost identical to the themes of "family, work, neighborhood, peace and freedom" that Reagan pegged in his 1980 acceptance speech as the basis of his successful campaign. But Matheson said the Democrats will argue that rapid changes in family structure, the domestic economy, international trade, defense needs and superpower relations require new policies and programs.

He promised that the full report, the product of a year of hearings by local, state and federal elected officials, will contain new ideas on everything from child care and pensions to military procurement and arms control. It will not, he cautioned, address issues currently before Congress.

This morning, Boston pollster Brad Bannon told the party leaders it is vital for Democrats to emphasize their receptivity to new ideas because "in the eyes of the public, the Democrats have come to represent the status quo, while Republicans have come to represent change and reform."

"Ideological tinkering" aimed at shifting Democratic policies to the center or right "won't help us," Bannon said, and young people especially are turned off "when Democratic politicians talk about protecting Social Security or American jobs . . . because protecting is such a status quo word."

A different perspective came from Rep. Don Bonker (D-Wash.), who headed the task force on trade for both the Matheson commission and the House Democratic Caucus. Bonker said trade "could be the hottest issue in the 1986 elections," because of the loss of jobs in import-affected industries. "If we are not in a trade war, there are skirmishes on all our borders," Bonker added.

He argued that the Democratic trade bill recently passed by the House "is not protectionist," despite editorial criticism of the measure and Reagan's labeling it a "Kamikaze" approach that invites retaliation from other nations.

The tone of the final meeting of Democratic leaders before the November election was notably upbeat. Party Chairman Paul G. Kirk Jr. led off a parade of predictions that Democrats will regain control of the Senate in November by gaining at least four seats.

State chairmen backed that forecast with assertions that private polls show Democrats leading in such Senate battlegrounds as Idaho, Louisiana, Nevada and Florida.

More striking -- and surprising -- were assertions that seemingly safe Republican senators in New York and Washington may face real challenges.

New York Democratic Chairman Laurence Kirwan cited a newly released Marist Institute poll that found only 38 percent of those interviewed saying they were committed supporters of Sen. Alfonse M. D'Amato (R-N.Y.). He said that if wealthy Democrat John Dyson, who devised the "I Love New York" tourism promotion slogan, wins the Senate nomination, "he can give D'Amato a real race."

In Washington, the slow-starting campaign of Brock Adams, a former House member and secretary of transportation, has finally come into focus, Democratic officials said.

Adams, who was last elected in his Seattle district in 1976, acknowledged earlier this year that he was "rusty." But he has stung Sen. Slade Gorton (R) recently for an "ineffectual response" to the Reagan administration's decision to make Hanford one of three possible sites for a second nuclear-waste dump. Noting that all the sites in eastern and midwestern states had been eliminated, Adams said, "Those states wouldn't be sending us their nuclear waste if Henry Scoop Jackson and Warren Magnuson were still in the Senate."

New York and Washington are uphill races for the Democrats, but party strategists made the point that if any of those "second-tier" victories materialize, they would almost assure a Democratic takeover of the Senate.

Meantime, the meeting heard upbeat reports about party fund-raising efforts and the national committee's assignment of two staff members for political organizing and finance to 16 targeted states.

State chairmen also said they have almost invariably been able to block followers of Lyndon H. LaRouche Jr. from winning Democratic Party nominations, avoiding the embarrassment Illinois Democrats suffered in the first primary of the year.