President Reagan called them "my own generation," and he told the senior citizens at the Angelus Plaza senior citizen apartments downtown here that he was stopping by to see them to clear up some of the "misinformation" about his stand on Social Security.

"If I was guilty of all the things with regard to Social Security that I've read about myself and heard said about myself," Reagan told the group of about 200 crowded into the cafeteria of the high-rise apartments, "I wouldn't like me either."

The group applauded vigorously when Reagan promised, "We're not going to let that rug be pulled out from under anyone dependent on that program." But when he opened the floor to questions it was not budget cuts or the problems with the federal pension system they wanted to talk about.

One man wanted to know why Reagan had changed his haircut. Reagan said he hadn't. It just looked that way when it was windy outdoors.

A woman wanted to know how he decided who to call on at presidential news conferences. And another who said she was in a musical comedy with veteran performers, all over 60, said she was complimented after each performance by people who said that she favored Nancy Reagan. She wanted to know what Reagan thought about that.

"Yes, I can see why they say that," Reagan told the dark-complexioned woman with a heavy Hispanic accent. "Yes, I can. Right. And I shall tell her," he said.

President and Mrs. Reagan flew here last night from their mountaintop ranch north of Santa Barbara to be with friends when the First Lady celebrated her birthday today.

Aides added to his schedule the short visit to the senior citizen house, an off-the-record lunch with top brass of the Los Angeles Times and a meeting with about 100 friendly state and local officials from 13 western states to sell his proposal for a New Federalism.

In the session with state and local officials, Reagan appeared to inch closer toward embracing the idea of a flat-rate tax on income, calling it "a very tempting thing."

"Let's all of us admit that probably there is more resistance to the income tax in America today, not from the amount of it, but from the complexity of trying to figure out what the amount should be," he said.

Asked whether he believed that the Federal Reserve Board was responsible for keeping interest rates high, Reagan responded, "No, I have to tell you we cannot make a scapegoat of the Federal Reserve this time. Since the first of the year, they have been working very hard on holding an even increase in the money supply."

Reagan told the local officials that he expected that Congress and the federal bureaucracy would mount opposition to his federalism proposal, which is still in the drafting stage, because it "will get rid of a gigantic layer of administrative overhead based in Washington, and maybe this is one of the reasons why so much of bureaucracy is opposed to this, because I think that poverty has become a career for a lot of well-paid people."

Reagan appeared to be expecting hostile questions from the senior citizens, saying that they probably had often said to one another, "Boy, if I could only ask him something or tell him something, I would say . . . . "

Instead, however, they seemed charmed by him and delighted by his visit. Several stood, not to ask questions, but to say how glad they were just to meet him.

Reagan warmed to the occasion, speaking as a defender of the "mores and the customs" of their generation.

"I get concerned sometimes that there is a tendency to throw away some of the values just because they are old, without recognizing that they have true worth or they would not be around," he said.

He recalled the time when he was governor and confronted University of California student leaders. They told him, Reagan recalled, that he could not understand their generation because he had not grown up in an age of jets and space travel.

Reagan said he responded, "You are absolutely right. Our generation, we did not have those things when we were your age. We invented them."