A few years back, Wilfred Barry got mad at the developers who were making handsome profits by improving raw land on the outskirts of greater Chicago.

Barry, who is president of D'Abar Builders of Downers Grove, Ill., figured out a way that he and some fellow builders could get some of those land profits for themselves. That was six years ago. Today, the price of improved lots is rising 20 per cent a year in Hinsdale County and joint land ventures among the country's builders are growing in popularity as a consequence.

Set up by the Northern Illinois Home Builders Association, the joint ventures take one of two forms. In each case the partners put up an equal amount of money to buy a tract, and improve it with loans from savings banks. (Banks often land on better terms to stable partnerships - where each one is liable - than to single builders.)

Then, according to HBA executive vice president Rober E. Langguth, the partners can draw straws for the lots immediately, each pay an equal amount, and dissolve the partnership. A second method is for the partnership to sell off the lots to builders as they find sales prospects for homes. Those builders who decide not to use the land at all can resell their lots to the partnership.

But as partners they will also benefit from the eventual sale of the land. A builder's share can also be sold to a third person if the partnership refuses it, but this rarely happens due to the scarity of improved land non-builer speculators are excluded.

The purpose of these joint land ventures, apart from dealing out developer profits, is flexibility for the builders. By buying into several ventures for the price of a single subdivision, he can build on tracts where there is the greatest demand rather than being constrained to do the entire subdivision in which all his capital is tied up.

For the home buyers, this also has an advantage. It means a choice of different styles within the same subdivision, not look alike houses by the same builder.