Seeking support from a constituency he has been accused of ignoring, President Carter came here today and offered a sympathetic ear to the ubran poor but little in the way of concrete proposals.

Carter, at the start of his most extensive domestic trip since taking office, came to a city plagued by some of the nation's most severe urban problems for 90 minutes of often rambling discussion on a variety of topics.

He was politely received, but on the issue of prime importance here and in other big cities - unemployment, particularly among young blacks - he could only acknowledge the difficulty of the problem.

Lawrence Hall of Gary, Ind., put it directly, as he and the President sat at a large rectangular table in the Veterans Memorial Building here.

"I don't feel much like talking about energy and foreign policy," Hall told Carter. "I am concerned about how I am going to live . . . I can't be too concerned about other things when I have a daughter to raise and I don't have a job and I'm 56 years old."

The President flew here early this afternoon, beginning a two-day cross-country trip to six states, to attend a forum on urban policy sponsored by the Community Services Administration. Hall, an unemployed steelwroker, was one of 13 people who sat around the table and talked to Carter for an hour about unemployment, housing discrimination and a host of other big-city problems.

The President said he came here to listen. He took notes, went out of his way to praise Congress for cooperating with him and repeatedly cited efforts by his administration and Congress to deal with urban problems.

But he brought with him no announcements of initiatives to deal with the problems discussed around the table, and he was bluntly pessimistic about the short-term prospects of a significant cut in unemployment.

Black Courtney Matthews told him: "My question to you is, what is a 20 year-old man to do when he wants to work and he wants to help his family and he wants to get a job in a city where there is no jobs for minority youth at all?"

"That's a good, tough question," the President replied. "I can't tell you I have the answer . . . It's going to be a long, tough proposition."

The fact that Carter had no answer for this or several other thorny questions caused Rep. John Conyers Jr. (D-Mich.) to tell reporters after the forum he was particularly upset that the President did not even mention the so-called Humphrey-Hawkins full employment bill.

The White House and congressional supporters of this legislation have been negotiating gor weeks. The bill would include a large measure of central economic planning aimed at reducing unemployment to a mandated level over a period of years. Both sides reportedly are close to agreement, but not close enough for Carter to mention it today.

Conyers said the President's participation in an urban policy forum in which the Humphrey-Hawkins bill was not mentioned "is the symbolism that did not get to the real point."

"I couldn't understand it," Conyers said. "I thought he was coming in here to announce that he was supporting" the legislation. "That's what everybody said around the table - they need some work."

Recalling that in early September the President said he expected to announce support for the legislation "in 10 days," the Michigan Democrat added:

"And then he comes to my city and my constituents, grossly out of work, and dosen't mention the full employment bill one single time. I feel I have been put on."

The 90-minutes urban policy forum was a low-keyed affair in a large room with about 400 onlookers. The 13 participants were chosen by the Whtie House and the Community Services Administration. Their comments were less questions or demands on the President than statements about the plight of the poor and polite requests for help.

After the roundtable discussions, which rambled for just over an hour, Carter took questions from the audience for about 20 minutes, often asking Graciella Olivarez, head of the Community Service Administration, to answer them.

Outside the building about 100 protesters, held well back and out of Carter's sight as he arrived, waved signs calling for more jobs. But most of the people the President saw today were friendly, and a threatened protest by Wayne State University students over U.S. policy in the Middle East never materialized.

From Detroit, Carter flew to Des Moines to appeal for enactment of his energy legislation. The Jefferson-Jackson Day dinner attracted about 3,000 people at $50 a couple.

The President's six-state trip, which will take him into fivcestates that he lost last November to then-President Ford, was planned as a mixture of politics and official business. He was accompanied today by the Democratic congressional delegations from Michigan and Iowa, and in both Detroit and Des Moines state party leaders turned out to greet him.

Carter's stop in Detroit was designed in part to counter criticism that he has not shown sufficient interset in the nation's big cities. He has already held highly publicized "town meetings" in Clinton. Mass., and Yazoo City, Miss., but, until today, nothing comparable in a major urban center.

This is also his first presidential trip into the Midwest and West, which Ford all but swept in November.

As expected, Carter sought whenever possible today to drum up support for his energy bill, although energy was not a dominant topic at the Detroit forum. He told Hall, the first person to address him at the forum, that "passage of the energy bill will provide an increasing demand for steel," and through such measures more jobs would become available in the steel industry.

Tonight, the President stayed at the home of Woodrow Wilson Diehl, a farmer in Indianapolis, a few miles from Des Moines. On Saturday, he will have breakfast with a group of farmers at the Diehl home before flying to Omaha to inspect Strategic Air Command headquarters, to Denver to participate in a roundtable discussion on water policy, and to Los Angeles to address a Democratic fund-raising dinner.