Downtown Los Angeles, which used to call the shots in this sprawling town, is about to begin an unusual campaign of selling its hopes for the future to the surrounding, and somewhat skeptical, region.

The pitch for improving Downtown's economy and quality of life comes in a strategic plan that calls for an additional 100,000 residents in the area, bolstered security, a night life of entertainment and dining, and vigorous efforts to increase industrial and white-collar jobs. It envisions thriving markets, more parks, a nicer pedestrian environment and fewer homeless people on the streets.

The plan repeatedly asserts that all of Southern California will benefit from such a vibrant and economically revived Downtown Los Angeles. "Downtown, the center of a powerful region, must be made healthy," the introduction declares.

But even as its authors prepare for the document's formal unveiling Tuesday, they acknowledge that the lingering recession, political resentment and suburban-oriented social trends may make their dreams difficult to realize.

"There may have been a time when a plan like this might have just focused on Downtown and sailed through and been implemented and all the rest," said Robert Harris, the USC architecture professor who co-chaired the 60-member citizen task force that wrote the report. In a Los Angeles battered by the 1992 riots and defense industry cutbacks, he added, "it is not the perspective of Downtown or nothing. We need to take advantage of the economic possibilities of all the districts of the city. There aren't any throwaways. And in that perspective, you wouldn't overlook Downtown."

The guidelines for Downtown development for the next 25 years do not carry the force of law and do not include funding mandates. Still, the plan must be approved by the Community Redevelopment Agency's board and by the Los Angeles City Council--both of which have changed dramatically since then-Mayor Tom Bradley commissioned the study in 1989 as the office market began to show the vacancies that plague Downtown.

And, of course, Bradley's Democratic Administration has been replaced by that of Republican Mayor Richard Riordan, whose personal ties to Downtown may be tempered by his political dependence on support in the San Fernando Valley and Westside, informed observers say. Mayoral aides report, however, that Riordan generally favors the plan.