The bureaucrats at the Economic Development Administration dug into their files yesterday for a defense against David A. Stockman's famous "black book," which writes them all out of jobs, and came up with a document that warmed their hearts.

It's called the "Stockman Letter," and dozens of photocopies of it are floating around the Commerce Department.

The letter is of the kind congressmen are always writing, seeking pork-barrel projects for the folks back home. But in this case the letter from Stockman the former congressman provides an eloquent defense of an agency that Stockman the Office of Budget and Management director and ace budget-cutter wants to kill.

The letter was written Nov. 30, 1978, in support of a $226,000 grant for an industrial park in Adrian, Mich., which EDA had refused to fund because the local county government hadn't put any money into it. The project, sponsored by the Greater Adrian Industrial Development Corp., Stockman wrote, "would couple private and public investment . . . EDA funds would be used as seed money."

"This is clearly the type of program that EDA should be funding," President Reagan's budget-cutter said. "The idea of utilizing public and private dollars for the development of a strong industiral base in areas of high unemployment should be a top priority.

"Your willingness to make funds available . . . in support of the city of Adrian's industrial park development project would be most appreciated. Thanking you in advance for your consideration, I am very truly yours, Dave Stockman, member of Congress."

EDA didn't get around to approving Adrian's grant until two weeks before last year's presidential election. By that time, inflation had increased the total cost of the project drastically, and the three separate EDA grants given the community totaled $461,945.

The grant was looked upon as a godsend in Adrian, a city of about 28,000 in southeastern Michigan where unemployment now runs over 12 percent.

"It's very helpful to us," said Jack Germond, an Adrian banker and longtime member of the board of the industrial development corporation. "We estimate it will put us about five years ahead of the schedule we would have had without it."

Meanwhile, in Congress, Stockman voted against continuation of EDA when it came up for reauthorization in 1979.

"He was lending his name to something that would lead to good will and votes," said Jack Bennett, executive director of the Greater Adrian Chamber of Commerce.

Stockman was behaving like most self-styled budget-cutters, says one hardened EDA official, who asked not to be identified. "It's in a great tradition. You vote against an agency and then turn around and milk it for all it's worth."

An OMB aide said yesterday that ther were many times during his tenure in Congress that Stockman opposed programs, but once they were inacted, "He tried to do his share to get a piece of the pie for his district."

She said Stockman had no comment on the 2-year-old letter.

In the book, he says EDA subsidies generally go to large, established corporations that can get capital elsewhere. The loans and grants, he says, "have little impact creating net new jobs and capital investment in the national economy." The agency, he says, should be terminated.

Asked about this, Adrian booster Germond said, "This is a pretty conservative area, and I tend to identify with Dave's conservatism. It is the same old story of whose ox is being gored."