Mayor Marion Barry has been house hunting east of the Anacostia River, and he's looking for more than a place to stay.

Barry has been shopping for a house in the Hillcrest area of the city near Pennsylvania Avenue and the Prince George's County line, a suburban-like cluster of large brick homes on grassy hillsides where many young, black professionals are now moving. They are the kind of people Barry feels he does best with politically and his advisers believe that he would be better able to solidify their support if he lived there.

Barry advisers said the mayor is trying to build on the slim political base he assembled to eke out a narrow victory in last year's three-way Democratic primary, and establish a broader-based organization that will ensure his political dominance in the future.

"Every mayor needs an organization," Barry said. "For a politician's survival, you have to have an organization. It's as simple as that. Any mayor who wants to be around needs one, and I intend to be around a long time."

The lastest success Barry is claiming for his organization is John Ray's victory Tuesday in a special election to choose a successor to Barry on the City Council. Barry actively endorsed Ray, and the Ray organization-including fundraisers, strategists and many ward workers-was virtually the same as Barry's own campaign organization of last year.

In Tuesday's election, Ray won Ward 7, the far Northeast and Southeast section of the city that includes the Hillcrest area, where Barry is now searching for a home. Barry lost that ward in the Democratic primary last September.

Sources close to the mayor said Barry himself wanted very much for Ray to win in Ward 7 because the mayor considers the area a thriving, heavily black and increasingly middleclass section of the city that already has the third highest number of registered Democrats in the city and could be pivotal in Barry's political future.

Barry was elected with a scant 34 percent of the vote and much of his support came from white neighborhoods. With several other city politicians scrambling to stake out political strongholds, Barry has focused on Ward 7 because of its potential.

"Ward 7 has been neglected politically," Barry said. "It has as many potential registrants as Ward 4 (upper Northwest Washington east of Rock Creek Park). In Ward 4, you've already got more political generals than you need." Barry is not one of them.

"Marion is looking down the road," one intimate said. "There are a lot of people beginning to vote along radical lines. Marion realize that success in this town in the future may depend on how many black votes you get.

"Marion is actively trying to build up that support and he is trying to make sure that people east of the river get active in politics. In the future, Wards 7 and 8 (Anacostia) can determine who gets elected," the friend said.

Barry's attempt to expand his political base beyond the liberal whites, middle-class newcomers, gay rights activists and feminists that swept him to victory in the primary comes as other city politicians are staking out their claims to other areas of the city with unique interests.

In Ward 4, City Council Chairman Arrington Dixon and his wife, Democratic National Committeewoman Sharon Pratt Dixon, worked hard in the special election to get Charlene Drew Jarvis elected as Dixon's replacement in the Ward 4 Council seat.

"It was very important to Arrington," one source close to Dixon said, "for a strong person to win in 4 and someone who was close to Arrington. It's the premier Democratic ward in the city, and it most typifies the majority vote-a black vote."

Building on ties to the established black middle class in Ward 4 as well as sentiments of blacks who have lived in the city for some time and feel threatened by Barry and some of his political newcomers, the Dixons are trying to solidify their base in the ward.

"There's a lot of people in this town who waited a long time to be enfranchised and they're not going to let anyone-black or white-tell them what to do," said one source close to Dixon.

The Ward 4 group has strong ties to Del. Walter E. Fauntroy, long considered the most popular city politician, who nevertheless failed in his effort last year to use his own popularity and organization to get former City Council Chairman Sterling Tucker nominated for mayor.

Fauntroy refused to discuss any of his political operations yesterday, though others said Fauntroy has been working to strengthen his own political base in Ward 5, the largely middleincome section of the city that includes most of Northeast Washington.

"It sounds like gossip to me," Fauntroy said.

The scramble for political control could come to a head next year, when city Democrats choose representatives on the D.C. Democratic State Committee and delegates to the Democratic National Convention.

Barry said he intends to play an "integral part" in fielding a slate of candidates. Committee Chairman Robert B. Washington Jr., who has been closer in the past to Fauntroy than to Barry, said he intends to do the same.

Some of Barry's supporters were also saying after the Ray victory in Ward 7-by a narrow margin of 106 votes-that it should be a notice to council member Willie Hardy, who has not supported Barry or Ray in the past, that she could be facing a tough fight for her job in next year's election.

"I think it might be a message," said Lorraine Whitlock, Barry's principal political operative in the ward. "Ward 7 is becoming politically aware. Ward 7 is anxious to get on the map.

"We're reaching the point where we are operating more at an intellectual level than an emotional level.We think the person on the City Council ought to be elected on competency and performance rather than popularity and name recognition."

Hardy could not be reached for comment yesterday.

One leading Democrat close to Dixon and Fauntroy, who asked not to be named, said, "They can try to take on Willie if they want, but they're gonna have to have a fight on their hands because Willie won't be by herself."

The recurring face-off between Barry and his political foes is in many respects the consequence of the sharply divisive Democratic primary in which Barry, Tucker and former mayor Walter E. Washington battled for nomination.

Since winning the primary, Barry has tried to unify the party behind him. But at each opportunity, some of the same divisions have resurfaced and in other cases, regular Democrats are still too bitter to come into the fold.

The battle lines often cut across ideology, program and past antagonisms. Ray's major opponent in the special election, for example, was former council member Douglas E. Moore.

Many Dixon workers labored for Moore, however, to make sure that Ray - and Barry - would be denied a victory on Dixon's home turf.

The area where Barry has been house hunting is one where houses sell for between $80,00 and $90,000. Barry said he has looked at four houses on Westover Drive SE, a large circular roadway on a hilltop overlooking Pennsylvania and Branch Avenues SE.

Among those living on the street now are developer H. R. Crawford, Howard University Administrator Bryant G. Harris and one of Barry's top housing aides, Sidney Glee. Barry said he looked at one house on Westover Drive with an asking price of $150,000 and decided not to buy it.

The mayor also said he is looking along Highwood Drive, which is across Pennsylvania Avenue from Westover. Among those living in that section are labor leader Henry Brock and Geraldine Boykin and former D.C. Office of Human Rights director James W. Baldwin.

A real estate agent who sells houses in the area said many young professional couples, including some whites, are moving into Hillcrest and replacing older, retiring whites. She said Westover Drive, from which some residents can look out of their livingroom windows and see the Anacostia River, the Capitol and some monuments, is becoming "one of the addresses" in Washington.

One Westover Drive resident chuckled at the thought of the mayor moving onto the street. "I hope he does," she said, "so we could have a gate that would block us off." CAPTION: Picture, MAYOR MARION BARRY . . . organization needed