The Rev. Jesse L. Jackson told a responsive crowd of fellow Baptists in Los Angeles yesterday that he will decide by October whether "we have the machinery, the masses and the money" to seek the Democratic nomination for president.

Jackson also asked pastors and other delegates to the National Baptist Convention, the largest black organization in the United States and the country's third biggest Protestant group, to help him register 3 million new voters and defeat President Reagan.

He said that 10 million of about 18 million eligible black voters were registered.

Jackson said he will decide "later this month or early next month" whether to run for the nomination, and said that his decision will depend on whether "we have the machinery, the masses and the money."

"So far," he conceded, "we do not have the money to mount a credible campaign."

Jackson said he was "seriously considering" the race, however, because of support from such black leaders as Mayor Richard Hatcher of Gary, Ind., and Rep. Louis Stokes (D-Ohio). On Wednesday, Rep. Edolphus Towns (D-N.Y.), former attorney general Ramsey Clark and former Manhattan Borough president Percy Sutton said they were forming the New York Jesse Jackson for President Exploratory Committee.