THE DEMOCRATIC field has its latest non-entrant. After traveling 75,000 miles around the nation, after launching direct-mail and house-party fund-raising efforts that brought in at least $1 million, after propelling herself to the middle of the field in public opinion polls, Patricia Schroeder returned home to Denver's Civic Center Park and announced she's not going to run.

She was obviously torn in making her decision. She could see that she was arousing genuine enthusiasm among a not inconsiderable constituency: "We rubbed two sticks together and started a political bonfire." She was raising more money from her direct-mail appeals than some declared candidates, and she was attracting large, cheering crowds -- an exhilarating experience even for a politician who considers herself as unconventional as Rep. Schroeder does. But she could not see a clear pathway to the nomination. "I could not figure out how to run," she said. "There must be a way, but I haven't figured it out yet."

Rep. Schroeder's artless, teary performance was not exactly inspiring. And her no-go decision will discourage some who hoped she would be the first serious woman candidate for president, although one might add that other women have run before, including Sen. Margaret Chase Smith, who, like Rep. Schroeder, served long and usefully on an Armed Services committee (in 1964), and Rep. Shirley Chisholm (in 1972). But there will be other woman candidates, and at some point one of them will win. Rep. Schroeder's problem, as she seemed to recognize, was more specific. Her enthusiastic constituency may have been large enough to enable her to run a spirited campaign, but it seemed too small to enable her to win the nomination. In the circumstances, she decided, sensibly enough, not to undertake a grueling effort that seemed almost certain to fail.

It was a conventional political decision from a politician whose successful career has been based on being unconventional. She was elected to the House in 1972, when few women ran, beating a Republican incumbent in a Republican year. Her constituency -- the city of Denver -- is disproportionately black, Hispanic and yuppie, safely Democratic and culturally liberal. She has been an outspoken and witty spokesman for those Americans who believe that most of their fellow citizens have been bamboozled by Ronald Reagan; it was Congresswoman Schroeder who dubbed him the "Teflon president" and prospective presidential candidate Schroeder who said Americans this year need a "rendezvous with reality." Rep. Schroeder sees herself as one who does not play by the old rules, who found herself "shuddering" when professionals "started talking about how you have to look presidential." But when it came time to make a decision, this politician who has had her share of accomplishments in a House where the game is no longer played by the rules of 1972 decided that she couldn't win in a presidential race played under the rules of 198