The Community Investment Fund, which President Carter described as a keystone in his urban policy, is 18 months old and this week, 1,000 savings and loans association executives and community leaders gathered in Washington to hear an update on the fund's activities.

The five-year, $10 billion program is aimed at revitalizing the country's older communities by using public funds funneled through thrift institutions to attract support from the private sector. To date, 910 S&Ls have received $3.05 billion in advances and commitments from the Federal Home Bank Board. Those figures are double what they were last February.

Three private dollars were raised for every public dollar invested during the first 18 months of operations. As a result, the 416 S&Ls that have been in the program for at least a year have invested $1 billion, which has helped create $3.3 billion in housing, or 104,510 units, it was announced.

As of December, the southeastern region, which includes Washington, has 140 participating S&Ls, 40 percent more than the next bank district. The amount of Community Investment Fund money drawn down by S&Ls in the Southeast totaled to $305.8 million, second only to the $374.2 million drawn down by the San Francisco region.

Other goals of the fund are to develop housing in rural areas, to confront the problems of displacement resulting from urban renewal, and to keep mortgage money flowing to those areas that are most in need during tight money periods. Examples of fund projects include home counseling for low- and moderate-income home buyers in Palo Alto, Calif., transforming an old school in Pennsylvania into apartments, and restoring a historic shopping center in Cleveland.

In the District, S&Ls have formed joint service corporations to build apartments and town houses.