Delegates to the Democratic Party's mini-convention later this month will be asked to vote on a "nuclear freeze" resolution.

The draft statement on national security that went out this weekend to the several hundred delegates to the midterm party conference in Philadelphia says "the Democratic Party welcomes . . . the nuclear weapons freeze campaign." It endorses negotiations with the Soviet Union for a "mutual and verifiable freeze on the testing, production and deployment of nuclear warheads, missiles and other delivery systems."

The statement also calls for "strict adherence by both sides" to terms of the SALT II treaty and other arms control agreements until "major, mutual reductions" of nuclear weapons are negotiated.

Meantime, it says, the United States should support a strengthening of its conventional forces to meet a Soviet buildup that "is continuing beyond any reasonable justification." But it derided the Reagan administration for "finding waste everywhere except in the Pentagon."

The national security language is contained in one of seven policy statements to be used as the starting point of debate in the issues workshops at the Democrats' third quadrennial midterm conference. It will be held June 25-27.

The resolutions will be subject to debate and amendment by voting delegates in individual workshops, but the workshop reports will not be subject to change or rejection at the convention's final plenary session.

The cover letter that went out with the draft resolutions from national chairman Charles T. Mannatt and vice chairman Lynn Cutler to the delegates said the statements are intended "to define the broad goals and principles" of the party, "not as party dogmas, nor an attempt to rewrite our platform."

For the most part, they are just that--replete with rhetorical swipes at the economic, fiscal, energy, environmental and social policies of the Reagan administration.

Mannatt and Cutler said in the letter the hope is to show "a strong and confident Democratic Party, ready to lead our nation forward out of a Republican recession." Democrats, they said, "reject the narrow, rigid ideology of trickle-down economics, unfair tax cuts and unwise program cuts."

The economic policy paper, in a sarcastic reference to President Reagan's 1980 theme, suggests that "perhaps the Republican theme for the election campaign this year will be, 'Are you better off today than you were in the Depression?' "

The Democrats criticized "untargeted tax cuts slanted heavily toward the rich" but do not explicitly call for killing or delaying the mid-1982 and mid-1983 income tax cuts to reduce the federal deficit.

The policy statements reaffirm the party's support for the Equal Rights Amendment, affirmative action programs and its opposition to anti-abortion amendments.

They deny Democrats are "wedded to a large central government for its own sake," but say Reagan's propsals to turn back responsibility from Washington "is not an agenda for making government work better. It is a war on state and local governments."

The nuclear freeze issue is one of the few new issues addressed in the policy proposals, and party officials said they anticipated it would not be a matter of major controversy among the mini-convention delegates. Half of those delegates are the members of the Democratic National Committee and the others have been chosen by Mannatt and state Democratic leaders.