Hilda Mason took an early but narrow lead over former D.C. School Supt. Barbara A. Sizemore yesterday in the special D.C. City Council election to fill the at-large vacancy created by the deaths of Julius Hobson Sr.

Early returns from seven of the city's eight wards showed Mason, who has occupied the seat temporarily since Hobson's March 23 death and had the backing of most of the leader's in the city's dominant Democratic Party, receiving 3,544 voices. Sizemore had received 3.520.

The preliminary and incomplete returns did not include any results from voting in the city's third ward, where Gyrex automatic vote counting machines were used. Those returns were expected later last night.

The ward three returns could be crucial because that ward, which includes affluent, predominantly white neighborhoods west of Rock Creek Park, has more voters than any other ward in the city and a traditionally higher voter turnout than elsewhere in Washington.

Republican Paul Hays was running a distant third, with 985 votes, while independent Susan Truitt had 862 votes. The totals for other candidates were: Richard Clark (independent) 407; Susan Pennington (U.S. Labor), 81; Wade H. Jefferson (independent), 45; James Clark (Jii Lunaa), 40; Frank E. Sewell Jr. (Statehood), 27; and Leo A. Murray (Statehood), 24.

City election officials predicted that only about 10 per cent of the city's nearly 225,000 registered voters would participate in the election.

A generally unexciting off-time and off-year campaign and the day's hot muggy weather, which virtually baked the pavement in front of some polling places, were considered two factors that kept the voters turnout low.

In some areas of the city, the few poll watchers on hand moved sluggishly in the hot summer sun or occasionally sought refuge beneath shade trees, fanning themselves with campaign literature during the lulls when no voters were coming.

Inside the voting places, many of which had only electric fans to move the hot and sticky air around, there were some periods of 5 to 10 minutes when not a single voter appeared. Even though most polling places had a traditionally heavier vote in the prework morning hours of 7 a.m. to 9 a.m., precinct captains interviewed said the morning rush was considerably less yesterday than in other city elections.

None of the 10 contenders expected a heavy turnout. As the day wore on, getting out the vote became a central focus of activity of the candidates.

It was in this area in that Mason, who like most of the other candidates, had never run citywide before, appeared to most benefit from the campaign workers and know how that came with the endorsements she received from most of the leading Democrats in the city.

Her supporters ran a continuous telephone campaign, putting potential voters to touch with Democratic precinct chairmen who could arrange rides to the polls for those who wanted to vote. In the city's second and sixth wards, members of the city's Gay Activists Alliance worked to help get voters out on Mason's behalf.

The campaign leading up to the first special election in modern city history began almost immediately after Hobsons death, when Mason was chosen over several other Statehood Party members to be Hobson's interim replacement on the Council.

Using her four-month interim stint as a chance to build visibility citywide, Mason quickly garnered strong support from city Democrats, who were forbidden from running their own candidate because Democrats already have two at-large Council members, the maximum allowed by city law.

Mason ran her campaign much like an incumbent, stressing her experience on the school board and in community groups, and sometimes, in the view of her opponents, avoiding stands on controversial issues. Hers was the best financed of the campaigns, but two-thirds of the $21,000 she spent came from Mason's own pocket.

Sizemore's campaign was built around her visibility as former D.C. school superintendent, with an emphasis on being "unbought and unbossed." She voiced her opposition to legalization of gambling and marijuana. Fired by the school board in 1975 much of Sizemore's support was expected to come from those who thought the board was wrong to dismiss her for alleged inept administration.

Running a low-budget campaign, she virtually ignored the traditionally vote-heavy and more affluent areas of Northwest Washington. Instead, Sizemore concentrated on working class and low income voters in the Northeast and Southeast sections of the city, where voting strength has been growing in recent years.

Truitt and Hays both pushed economic development as the major issue facing the city. Truitt based her campaign appeal partly on the visibility she had gained during 15 years as a television reporter and another year as press aide to former Department of Human Resources director Joseph P. Yeldell.

Hays, the Republican candidate, had hoped his otherwise vastly outnumbered party could benefit by the absence of a Democratic candidate and the Republicans' own experience at turning out voters.

Richard Clark was the only one of the other six given recognition by city political observers as having any change of winning, based largely on his experience in two previous unsuccessful campaigns for the City Council seat from ward four.

The short, 4-month Council campagin raised no major issues that clearly divided the 10 candidates. It failed to attract much financial support from the city's business community, which is usually the prime source for campaign funds.

Although 99 per cent of the votes were expected to be totaled by early this morning, it will be at least two weeks before all of the returns - including absentee and challenged ballots - are certified by the city's election board. Only then can the winner be sworn in to complete the remaining 18 months of Hobson's term.