DENVER--Gary Hart, standing coatless before the snow-capped Rocky Mountains, announced his bid for the 1988 Democratic presidential nomination yesterday and promised a return to American ideals and a "presidency you can be proud of."

The 50-year-old former Colorado senator opened his second presidential candidacy stressing idealism and the power of ideas, themes that almost wrested the 1984 Democratic nomination from former Vice President Walter Mondale.

This time, it is hart who is ahead in the early polls, with the rest of the still-increasing field of candidates bunched far back.

"I intend to be a candidate for the presidency of the United States in 1988 and I do so for one single reason: and that is because I love my country," Hart said as he stood in Red Rocks Park for the morning announcement.

Later, Hart asked several thousand supporters at a rally in downtown Denver to give him their help and their time: "You give me 20 days in the next 20 months and I will give you a presidency you can be proud of."

Invoking the idealistic rhetoric of John F. Kennedy, Hart concluded:

"Let us go forward from this day committed to restore this land to all of its people, to restore a sense of genuine true patriotism to America. And if we do, we will have done the greatest thing for this country any of us could ever do.

"March on !"

His formal announcement at Red Rocks, a park 16 miles from downtown Denver, was before his wife and daughter, reporters, cameras and staff. Hart said the Park, begun with federal funds during the Depression, "is a symbol of what a benevolent government can do."

"Sadly, in recent years we've fallen far short of the ideal of America," Hart said. "We've let personal greed replace a sense of social justice and equity and the national good. We've let right-wing ideology skew this nation's basic priorities. We've increasingly let narrow special interests finance our campaigns and control our political process.

"Most of all I think we have lost a sense of the national interest and are in serious danger of letting our future pass us by."

Hart, Known in the Senate for his work on military reform and arms control, warned that domestic policies must not be shortchanged as he said they have been under President Reagan.

Hart is the third candidate to formally join the Democratic Presidential competition, joining former Arizona Gov. Bruce Babbitt and Rep. Richard Gephardt of Missouri.

Massachusetts Gov. Michael Dukakis, Sens. Paul Simon of Illinois, Albert Gore Jr. of Tennessee and Joseph Biden of Delaware, and the Rev. Jesse Jackson will enter the race later this spring. Arkansas Gov. Bill Clinton is still considering a bid.

Hart's 1988 effort is dogged by questions about the $1.3 million in debt remaining from his 1984 bid. But the campaign raised $400,000 for 1988 in a Sunday night dinner and promised to pay off the debt by early next year.