The city government put 2,835 properties with delinquen t real-estate taxes on the auction block this week, and two kinds of people came to the police lineup room to bid on them - the amateurs and the professionals.

The professionals were the ones that came for all three days of the sale, carrying thick looseleaf notebooks under their arms, with notations beside each property. They were also the ones who generally did not like giving their names to an outsider or explaining why they attended the tax sale every January.

Most of the amateurs came just the first day, and they carried only the list of delinquent properties that the city government had published in the newspapers Dec. 18. They were also more willing to talk.

"There's always less (amateurs) the second and third days of the sale," said Alfred Richards, acting chief of the property assessment division, who is in charge of the sale and has watched the newcomers come and go over the years.

"People hear there is a tax sale and they hear from a 10th cousin they bought some good property at a tax sale once, so they come down. They see all those people bidding, and they ask questions about what's going on.

"Most are interested in trying to get property," Richards said, but the real attraction of the sale for those in the know is the investment potential offered by the city. He explained:

The successful bidder at a sale must give the city government the amount of taxes due on the property, and while the city holds this money it earns interest at the rate of 1 per cent a month.

The delinquent property owner has two years after the tax sale to pay his taxes and redeem the property. Most properties, especially the desirable ones, are redeemed. Upon redemption, the bidder is given back his original payment plus up to 24 per cent simple interest for two years.

Carroll O. Little, who took annual leave from his job as a maintenance supervisor with the General Services Administration to attend the sale, his first, understands these economics, though he is an amateur.

"I can't lose anything," he said. "The rate of interest they pay back you cannot get from a bank or a savings and loan," he said.

A woman employee of the Department of HOusing and Urban Development who sat two rows behind Little, did not understand. Nevertheless, she asked not to be identified because she had told her boss she was going to the dentist's office.

"I don't know whereI bought or where the property is," she said. "I have to find them now." She also said she had never heard of the tax money earning interest.

Theodre J. Sheve and his wife, Geraldine, are not amateurs. They have been coming to the sale for the last 20 years, by Scheve's estimate.

Last year, the retired building contractor bought 345 properties, the largest number, and sent the city a check for $145,470 to cover his, purchases.

The Scheves know exactly where their purchases are."I have a knowledge of the city. There are certain areas you feel are more desirable to bid on than others," he explained. He doesn't bid on properties "in the ghetto or the slums," but added, "it looks like the slums are coming up."

Elbert J. Robinson, a lawyer, is also one of the regulars. Last year he bought 260 properties for $222,370. He refused to talk to a reporter during this year's sale and said he wanted no publicity.

Richards said Robinson has told him he bids on the property for the investment. Robinson usually bids on the property with expensive houses, because this is the property that owners will more than likely redeem allowing Robinson to recieve the amount of taxes back plus interest, Richards said.

A representative from Monarch Novelty Co., at 1331 14th St. NW., is another regular. The Monarch representative, the third largest bidder at last year's sale with $100,143 in property, refused to give a reporter his name during this year's sale.

The city tax department has rubber stamps with the names of all he regulars - because they know they will buy the majority of the property, especially during the last day after, the amateurs have retired.

The sale resembles a club meeting last year there were only 20 buyers about the same number that came this year. The regulars all know each other. Some chat amicably with each other and joke about who is the largest purchaser.

There are certain unwritten rules of courtesy among the regulars.

During the first day of this year's sale, one of the regulars, for example, stated publicly that he held a first mortgage on a property that was up for sale. That conveyed to the others that they should not bid because it could mean the first motgage investment might be lost.

Also during that sale, real estate dealer Leonard Freedman asked that because a friend who is mentally retarded holds a first mortgage on them and the properties are his major source of income. The others complied.

"I got a kick out of it," Little said after his first day, but he had no illusions. "It's really monopolized by the big real estate brokers because they have the bigmoney so they can bid no end," he said.