Last summer, after a personal telephone call from Prsident Carter, Patti Knox quit her job in Detroit and moved to Washington to preside over filling up to 300,000 census-taker jobs through Democratic Party patronage.

Today, Knoxis back in Detroit and out of work, the accidental victim of Carter's civil service overhaul.

It was Knox who discovered, only weeks after she arriveed, that the Civil Service overhaul act apparently prohibited filling the census jobs through patronage.

No one at census seemed to have noticed.

"I don't feel cross with the White House. I feel cross with the people running the cenusus," said Knox.

Knox's involvement with the disappearing patronage system began last summer when she was approcached by presidential assistant Tim Kraft, who asked her to set up a system for dispensing cenusus-enumerator jobs for the 1980 census. "I said I didn't care to do it," said Knox, an early supporter of Carter and director of public information for Detroit Mayor Coleman Young for three years.

"Then the president called, and I felt honored," Knox said. After some duscussion with her husband, she quit her job, left her husband and grown son in Michigan and moved to Washington at her won expense.

A few weks after whe arrived and settled into an apartment here, Knox discovered the change in the law that wiped out the job she had come to do.

"I think she told me. That was the first I knew about it," said Jim Turbitt, associate director for administration and field operations at the Census Bureau.

"We hadn't seen the legislation and no one from here had participated in the hearings," said Turbitt.

Knox said she discovered the change accidentally while reading the Civil Service overhaul legislation "three or four weeks" after she arrived.

Under the old patronage system, the party in power used its local party structure to find people to go door-to-door for the census. Those who met census requirments were hired and accounted for about 40 percent of the work force.

People who were referred through the party structure "were interested in politics. They were interested in and cared about the people who referred them and did a particualrly good job," said Knox. Knox predicted chaos when the Cenusus Bureau tries to hire 300,000 temporary employes without the referral system.

With the referral system, which she said would have provided a more qualified pool of people to choose from, the Census Bureau had expected to test more than a million applicants to get the employes it needed, she said.Now, "they could test several million people," she said.

"For them, it's a major thing to have watched out for," Knox said of the Census Bureau and the change in the law.

Knox said she was offered other opportuities to stay in Washington with the government but declined them. "I had a call from the president of the United States. I felt an obligation to come and I wanted to do the job. Now that it's not there, I felt no obligation to stay," she said.

As far as the outcome of the adventure is concerned, she said she felt like Adlai Stevenson when he once described his reaction to an election defeat: "It hurts too much to laugh, and I'm too old to cry."