Veteran Alexandria City Councilman Nicholas A. Colasanto yesterday lost his bid a fifth term on the council in a Democratic primary.

In an unusually light vote, Democrats named incumbent councilman Donald C. Casey, 40, and five political newcomers as candidates for the six seates on the council that will be decided in a May 1 general election.

Colasanto, 74, a former vice mayor of Alexandria, was the only council member to be indirectly touched by the city's bingo scandals last year. A Colasanto aide resigned after he was convicted of misdemeanor bingo offenses.

A crusty and controversial figure, Colasanto finished seventh in a field of eight candidates for the six at-large council seats.

In addition to Casey, the Democrats nominated Barbara Joseph, 41, Nelson E. Greene Sr., 64, James P. Moran, 33, Ron Williams, 31, and Marian Van Landingham, 41.

Roger E. Wheeler, 58, finished last.

After the vote was counted last night, Colasanto said: "I'm sad. I didn't want to lose. My political career is over."

He denied that his age or ability or the bingo scandals caused his rejuction by the voters. The only issue on which he focused last nihgt was one involving a duplex apartment building he owns on E. Custis Avenue, which he has repeatedly refused to repair since it was declared "unfit for human habitation" last October. Colasanto remarked that neighbors' complaints about the structure's condition "certainly didn't help me." Although Colasanto takes pride in publicly declaring himself a wealthy man, he has defended his right to own the building without improving it.

The unofficial totals show that 5,702 people voted yesterday, out of a possible total of 43,000.

The top vote-getter was Greene, a black funeral home owner, who received 3,716 votes. The next highest vote-getter was Moran, a U.S. Senate staff budget analyst, who received 3,286 votes. Van Landingham received 3,264 votes; Casey, 3,081; Joseph, 2,949, and Williams 2,545.

Greene got at least twice as many votes as his nearest rival in five precincts and three times as many as the next strongest finisher in a sixth. This seems to indicate he was the beneficiary of so-called bullet voting in which a candidate's supporters cast ballots only for him. City voters could vote for up to six of the eight candidates on the ballot.

Colasanto, who was first elected in 1963 and has served continuously with the exception of one term during the years of 1970-73, received 1,752 votes. Wheeler, the former head of several civic associations, received 1,588 votes.

Earlier yesterday, Alexandria Mayor Frank E. Mann formally filed papers for reelection as an independent. He will be opposed by former Mayor Charles E. Beatley, who won the Democratic nomination without opposition.

The council candidates nominated yesterday will oppose a Republican slate consisting of incumbent Robert L. Calhoun, David Speck, Rose Berler, Margaret Inman, Robert Hammerman and Carlyle C. Ring Jr.

Independents who have filed to run in the May 1 general election are incumbent council member Ellen Pickering, William Hurd and Alice Morgan. Morgan, a 35-year-old social worker who recently resigned from the city planning commission, announced her candidacy yesterday.

The top fund-raiser in the Democratic primary was Van Landingham, who raised $8,514.97, and was closely followed by Greene, who raised $7,909.53. Moran raised $4,411, and Colasanto raised $3,759.90, mostly by a $3,524.90 loan from himself to his own campaign.

The money raised by the other candidates were: Joseph, $2,886.80; Casey, $1,960; Williams, $1,725, and Wheeler, $200.