A colorful field of 10 candidates with widely contrasting views and differing political styles are vying in the July 19 special D.C. City Council election - the first local special election in modern city history - to fill the at-large vacancy created by the death of Julius Hobson Sr.

There is, for example, former D.C. School Supt. Barbara A. Sizemore, who got fired trying to change the city schools and now says she wants to change the city; and Susan Truitt, who used to be the buffer between former Human Resources Director Joseph P. Yeldell and the press and now says she thinks the government should be opened more to the people.

There is Richard R. Clark, a Republican turned independent; and Frank E. Sewell, Jr. a Democrat turned Statehood Party, who accuses one of his rivals, former school board member Hilda Mason of being a "bunny girl" because she's "hopped from educator to legislator." (Mason calls that experience).

There are candidates whose campaigns appear to be rooted in deeper social causes, like the sharp tongued independent James Clark, who attacks his audiences for not doing enough for the city's blacks and poor; and the U.S. Labor Party's Susan Pennington, who thinks local government efforts should be viewed in relation to national political and economic thrusts.

The low visibility of the campaign so far stems in part from the fact that many of the candidates are political neophytes running in an off-year, off-time election with a very short campaigning period. From the time of Hobson's death March 23 until the moment the last ballots are counted, only four months will have elapsed the time it takes most campaigns to get revved up.

There are only five weeks remaining before election day and still it is uncertain just who will be on the ballot. The D.C. Board of Elections and Ethics and D.C. Court of Appeals still have not decided if the challenges to three of the 10 remaining candidates are valid. One hopeful - Naomi T. VanderJagt - already has been stricken from the ballot.

Nevertheless, the election to fill the remaining 18 months of Hobson's four-year term comes at a time when major issues are confronting the city's young home rule government.

The city is strapped by financial woes that are leading to cutbacks in some essential services such as street lighting, alley cleaning and health and medical care. Property assessments have soared to a point where further tax increases are virtually a political impossibility, and it is uncertain how much financial assistance will come from the federal government.

Far reaching socio-economic issues face the city government, such as how to revitalize its housing stock without the controversial rent-control legislation of past years while still not seeing poorer families displaced by skyrocketing rents and speculative rehabilitation in older city neighhorboods.

The winner of the special election is likely to face legislative decisions on how to stop sex-oriented businesses from spreading into traditionally residential neighborhoods and whether marijuana use should be decriminalized. IN allition, there is a growing concern with the integrity of D.C. city government in the wake of recent controversies that have developed around several high-ranking city officials.

Most of these issues have arisen during question and answer sessions at forums for the 10 candidates. Others are implicit in the way the contenders are presenting themselves to the voters.

The early favorite in the view of city political observers is Hilda Mason, the 61-year-old former teacher and school board member who was appointed to fill the Hobson vacancy until after the special election.

A small, wiry figure with a salt and pepper Afro, her pitch to the voters is a simpler one: after 19 years as a teacher 5 1/2 years on the school board and untold years in a host of community and civil rights campaigns, she says, she has been there.

"I think from an experience point of view that I stand head and shoulders above everyone else that's running," she told one audience.

Mrs. Mason, the endorsed candidate of the D.C. Statehood Party, already has got the support of four of her 12 colleagues on the City Council and several key members of the D.C. Democratic Party.

Some had expected a fiery campaign between Mason and Sizemore, whom Mason helped to fire as school superintendent, but so far Mrs. Sizemore has avoided frequent attacks on Mason. Instead, Sizemore has focused her attack on the present attitude of government, proclaiming that the city needs "a bold and enlightened leadership willing to champion new ideas to answer some old problems."

The 49-year-old educator, who vocally targeted her school administration's efforts at blacks and the poor, has now broadened her approach to include property owners, senior citizens and "the poor of all races."

Her campaign pitch, nevertheless appears aimed at getting some votes from those who backed here during the stormy controversy over her stewardship of the city's school system. "I'm running as an independent because I am independent," she says.

Truitt, a 40-year-old journalist, who was a television reporter for 15 years, won an initial victory when the D.C. Democratic State Committee chose to endorse no one. Had the committee backed Mason it would have hurt Truitt, who is pitching toward the same moderate constituency, with a base in the upper northwest section of the city.

Truitt's general theme is that the citizens of the city need to get "their money's worth" out of their government. She is emphasizing the need for greater efforts to spur economic development in the city thus lessening residential property tax burdens, and improve public access to information from city government.

There are two Clarks in the race, but politically they have sharply different approaches. Richard Clark, 40, is a lawyer who twice ran as a Republican for the fourth ward Council seat. When the party failed to endorse him for this race, he registered as in independent.

"The only ax that I have to grind is against the present system we have," Clark told an audience last week. "Money is the issue, because all of it is going out and nothing is coming in." Clark thinks they city should "tighten up the screws on welfare cheaters" and revise its personnel system.

James Clark, 38, is a pharmacy technician at George Washington University Hospital running as an independent who says he represents the city-wide Jii Lunaa or Poor Peoples Party. Clark said all the 4,000-plus signatures on his petition came from unemployed persons. He plans to use large cardboard black crosses as part of his campaign material to symbolize that blacks are being "crucified on an economical cross."

Paul Hays is the endorsed candidate of the D.C. Republican Party. At assistant bill clerk in the House of Representatives, Hays says lightly that his experience in federal government has made him "a seasoned voice even at the ripe old age of 31."

He feels the city should place new emphasis on economic development and planning in its neighborhoods. The city government must set an economic agenda, he says, and be more responsive to its residents.

Wade H. Jefferson, a 48-year-old DHR employee, running as an independent, also feels the city has lost touch with its people. "I know the government from the bottom up," he says, and "this government is the worst I have ever seen."

Sewell, 23, says he is for "social change" and against the use of hollow-point bullets by the city's police department.

Pennington, 35, who ran unsuccessfully for D.C. delegate in 1974 and 1976 and for the school board in 1975, has sharply attacked her opponents who favor marijuana decriminalization.

Leo A. Murray, who has filed petitions to run as a Statehood Party candidate, could not be reached for comment on his platform and has not appeared at candidates forums where Washington Post reporters were present.