Invoking the Lord, pillorying Jesse Helms and imitating slurred talk by Republicans "drunk at lunch," D.C. Del. Walter E. Fauntroy was campaigning hard -- before a group of black Baptist preachers in Greensboro, N.C.

It was more soapbox sermon than speech, from a man who continues to preach Sundays at the church of his boyhood, the New Bethel Baptist Church in Washington's Shaw neighborhood. And hundreds of the black pastors and church activists responded with the cheering and clapping of confirmed believers.

Unopposed for his eighth term as delegate to Congress from the District of Columbia, Fauntroy, 51, has spent most of this election campaign stumping for others in such places as South Carolina, Alabama, Mississippi, Pennsylvania, Virginia and Illinois. In North Carolina, he went all-out for senatorial candidate James Hunt and other Democrats.

Since his House office has no voting rights, he is trying to gather chits for himself and the District.

"I want you to speak to the 400,000 Baptists of North Carolina," Fauntroy told his Greensboro audience. "Tell them what the Master would say: 'Beware of false prophets who come to you in sheep's clothing,' " he said, warming to the topic. "They Republicans want prayer in the schools, yet in their hearts are they ravenous wolves, even to cut the hearts out of the poor."

Fauntroy's approach to his job has been praised by some as doing a lot with a little, and criticized by others, who say his role is little more than that of glorified lobbyist for the legislative agenda of D.C. Mayor Marion Barry.

"He Fauntroy is a good spokesperson for a cause. . . . Rally the troops and that type of thing. But he doesn't spend time on his homework," said one local lobbyist who has dealt with Fauntroy for years. "He never understood any of the basic type of issues we were trying to deal with. . . . He would do whatever the mayor wanted done."

"I think he does a good job with the tools he's got and the limitations" that are placed upon him, said City Councilman John Wilson (D-Ward 2). "There is very little one can get done, but be a lobbyist for the city."

Aspirations to national prominence in political circles and his active role among national black groups keep Fauntroy on the road. "One of the things I often run into is the perception that 'he doesn't care about us locals, he's always gone.' That troubles me, because I am vulnerable there," Fauntroy said in an interview.

"In order to be effective here, I have to be a factor in the minds of the members of Congress . And I'm not a factor in the minds of the members if I'm going to every tea in Washington," he said.

He claims to have a nationwide network of 100,000 supporters who will write their representatives on behalf of D.C.-related issues. He says this network helped pass the Martin Luther King holiday bill and the D.C. Voting Rights Amendment.

Fauntroy spent a good deal of time this year as a key strategist in Jesse L. Jackson's presidential campaign and had hoped to become a senior policy adviser to Democratic presidential nominee Walter F. Mondale. But, Fauntroy said, Mondale failed to meet certain conditions Fauntroy had laid out for his participation. However, sources in the Mondale and Jackson camps said the problem was that Fauntroy had been too public about the role he would play before any agreement was reached.

The main congressional goal for D.C. since June 1983 was resolving questions about the city's authority to govern itself, an issue that arose out a Supreme Court ruling invalidating some legislative vetoes of D.C. actions.

Clarifying legislation went easily through the House but was stopped dead in the Senate when the Reagan administration announced its opposition. That started a year of intense negotiations, mainly between the Justice Department and city officials. In a surprise move, the administration dropped its opposition in the final days of the last session of Congress, and the measure was passed.

The mayor's lobbyists made frequent visits to the Hill and Barry met with presidential counselor Edwin Meese III. "In the last few hours, the mayor was the one meeting with Meese," Fauntroy acknowledged.

"I felt that . . . on the critical question of the Treasury borrowing and on the critical question of the bond issue, that he as an administrator would be able to add more it to it than I had been."

But Fauntroy disputes the notion that he did not take the initiative on other issues resolved this year. These issues included how and when to transfer control of St. Elizabeths mental hospital from the federal government to the city and the relocation of the Capitol Architect's greenhouse to make way for the Metro Green Line.

"These are items that have been on my agenda for years," he said.

But the main proposals on the St. Elizabeths question emanated from the Reagan administration and the mayor's office.

"He [Fauntroy] did serve as [a] great compromiser between the administration and the mayor" on St. Elizabeths, said one House staff aide. However, "There definitely is the perception that he is just pushing what the mayor wants," the aide said.

At the start of the 98th Congress, Fauntroy issued a legislative agenda containing about a dozen items. Only one, a routinely passed annual federal payment, passed.

Some of the city's "wish list" got sidetracked by the home rule crisis. Others easily got through the House but died in the Republican-controlled Senate. Those included bills giving the mayor authority to appoint D.C. judges -- now nominated by the president -- and a bill to transfer ownership of RFK Stadium to the city.

"I view my role as attempting to expand the powers of the locally elected government," Fauntroy said, adding that he has not been at odds with the mayor on any issue in this Congress.

Fauntroy supplements his $72,600-a-year salary by giving speeches around the country. In 1983, he made $35,480 in honoraria and gave $16,017 of this to charity, according to his latest financial disclosure report.

By mid-October, he had spent all but $3,000 of the $32,794 he raised for his general election campaign, according to his Federal Election Commission report.

No one has emerged as a serious challenger to Fauntroy in years. And a who's who of the city's leaders paid elaborate tribute to Fauntroy at a birthday breakfast this year.

But Fauntroy said that what stuck with him about that breakfast was his son, Marvin, 20, noting that his family had taken only one vacation in his life. "I was sick about it all day," Fauntroy said.

For the first time, he started ticking off events that had taken priority over vacations since Marvin was born: the Selma civil rights march in 1965, the King assassination in 1968, various campaigns.

It has started him thinking every so often about stepping down from the job, Fauntroy said. "Maybe it's time to slow down," he added.