Private donors are stepping in where the federal government is not to help community development groups pay for projects aimed at revitalizing urban neighborhoods.

The Ford Foundation and six major corporations and lenders have created the Local Initiative Support Corp., which has begun a two-year funding program of $9.35 million for the economic, physical and social improvement of participating communities.

The corporation's technical assistance, investments and matching seed money are expected to generate hundreds of millions of dollars more in private and governmental grants and investments. Officials predict that as many as 100 communities will be aided in the next five years.

The timing of the creation of the new organization -- just after Miami was rocked by rioting -- underscores the gravity of problems facing urban neighborhoods from Liberty City in Miami to Harlem and Bedford-Stuyvesant in New York City and Watts in Los Angeles.

"It is easy to say Miami was a tinderbox," said Franklin A. Thomas, president of the Ford Foundation, as he announced the establishment of the LISC, which will be headquartered in New York City. "Many cities are tinderboxes across the country.

"A dozen major community development corporations, such as the Watts Labor Community Action Committee in Los Angeles, the South East Community Organization in Baltimore and the Spanish Speaking Unity Council in Oakland, have been assisted by the foundation for a decade or more.

"Now hundreds more community organizations have arisen, large numbers of which demonstrate clear potential for comparable success," said Thomas. "Reinforced by the human and financial resources of large corporations and government, they can fulfill the promise of efficiently promoting residential, commercial and industrial development and delivering important community services.

"These initiatives are among the most exciting positive forces for social advancement in the nation. LISC was conceived as a means of helping these organizations draw the needed resources to their efforts and use them effectively. The foundation is glad to join with the corporate sponsors of LISC in this major demonstration of private-sector collaboration for constructive social change."

The Ford Foundation will provide $4.75 million in funding for LISC, according to Thomas. Corporate donors include the Aetna Life and Casualty Foundation which is donating $1 million; International Harvester Co., $750,000; Levi Strauss and Co., $500,000; Continental Illinois National Bank and Trust Co. of Chicago, $250,000; Atlantic Richfield Foundation, $100,000, and a $2 million "below market loan fund" from Prudential Insurance Co. of America.

Thomas hailed the formation of LISC as "a testament to the large and growing number of successful local organizations that are ready to expand and diversify their community development programs.

"This effort builds on a solid record of achievement by men and women who are directly affected by adverse conditions in all kinds of communities," Thomas said. "Residents of poor and middle-class black, Hispanic, Oriental and other ethnic neighborhoods have for several years displayed energy, imagination and leadership in arresting decline and making their communities substantially more livable."

In its first year, LISC will identify about 20 local groups and provide them with technical assistance in designing, financing and operating their project and in managing their own staff work and finances. The LISC will also help in securing investments and loans and grants from government, and core support grants to be matched dollar-for-dollar from local sources.

Five years from now LISC is expected to be supporting up to 100 local organizations in these ways, according to Thomas.

The chairman of the board of LISC is Robert D. Lilley, retired president of American Telephone and Telegraph Co. The chief executive officer is Mitchell Sviridoff, the Ford Foundation's vice president for the Division of National Affairs, who will be serving on loan to LISC.

Sviridoff joined the Ford Foundation in 1967 after serving two years as New York City Human Resources administrator under former mayor John V. Lindsay.