A few years ago, when gamblers at the pool hall at 14th Street and Florida Avenue NW ran short of money, they would simply excuse themselves for a few minutes, cross the street, and rob Mildred Harris at her corner liquor store.

All that ended abruptly two years ago. Harris now recalls with relief, when the city razed the pool hall as part of its 14th Street urban renewal plan.

For Tyrone Thompson, who owns a clothing store on 14th Street and lives on 15th Street, it used to seem as if "everytime I turned around someone was breaking into my car. Now, as soon as we get a few whites in the neighborhood, I don't lock my car because there are so many police around."

Up and down the 14th Street corridor, long the city's leader in crime and vice, residents, businessmen and workers are noticing the same thing: the crime rate is tumbling. A combination of urban renewal, private renovation of older homes, an unflux of more affluent residents, and a veteran force of police officers assigned to the neigborhood's 3rd Police District is apparently transforming the one-time slum area into a stable community.

Shaped like the state of Iowa, the 3rd District lies in the heart of the city bounded by Fourth Street on the east, L Street on the south, Connecticut Avenue on the west and Harvard Street on the North.

These boundaries contain the home of D.C. Mayor Walter E. Washington Howard University, the Washington Hilton Hotel, 34 embassies, the notorious drug corner of 14th and T Streets, the prostitutes at Logan Circle, the city's Latino section at 18th and Columbia Road and some of Washington's worst slums.

The city honored efforts of the district's 457 officers earlier this month when it awarded their commander, Deputy Chief Charles E. Rinaldi, the quarterly crime reduction award. The district has received the award twice in the last few years.

The award is given quarterly to the police district reducing its crime the greatest amount between a current quarter and the same quarter in the preceding year.

Although the smallest of the city's seven police districts, the 3rd led the city in 1972 (repeating in 1973) with 16,742 reported crimes, a figure that included the most murders (58), assaults (1,366), burgarlies (2,765) and robberies (1,996).

By last year the district had fallen to second place in city crime statistics, with 12,254 reported incidents. Assaults had dropped to 856, burgarlies to 1,750, and robberies to 1,410.

"It's not half as wild as it used to be," said David Budd, who grew up near 18th Street and Columbia Road and now works as assistant manager at Outlook, a men's clothing store, at 1767 Columbia Rd. NW.

"A couple of years ago people didn't come out that much," he continued. "People stayed in because you had people running around here robbing people . . . Now people are coming out again and staying in this area. They can put money in their pocket and they don't have to worry about people yoking them and and sticking them up."

The growing attraction of the district's aging two- and three-story Victorian homes, which line many of th area's blocks, to affluent bargain hunters has, in fact, contributed to the lower crime rates as well, officials said.

"They (the new residents) are more vocal about reporting crime and they cooperate with the police," said Oliver Neslage, who has lived in the Connecticut Avenue area since 1963. Neslage is also chairman of the Citizens Advisory Commission to the 3rd District.

When realtor Barbara Rothenburg, who lives at Logan Circle, moved into her 15-room house five years ago, prostitution and its related crime strangled the area.

Out of frustration, she organized the Logan Circle Community Improvement Association. "The pressure of the new people moving in got the older people interested, too, and they got braver," she said. "They thought it had always been this way and it could not be helped."

For the last month the 3rd District has saturated the area with an eight-officer squad and most of the prostitutes have moved elsewhere to escape police scrutiny.

"If you get the prostitutes," said chief Rinaldi, "they are the rats. Get rid of them and the other vermin that accompany them also leave the area."

Rinaldi and several citizens also attribute the falling crime rate to the large number of veteran police officers in the district and improved relations between police and citizens.

No rookies serve in the 3rd District, Rinaldi said. Even the newest officer has at least three years experience on the force. Most have five or six years, he said.

In December 1977, Rinaldi carved the district into 18 new beats for scooter patrolmen. Under the plan, the same officer patrols the same area during his shift. They get to know the area and, in turn, "the people know who belongs to them," the commander said.

Rinaldi said he tries to keep police officers highly visible in the district. "If you show the criminal you are out ther, he'll think twice about committing that crime, because nobody wants to go to jail," Belinger said.

Meanwhile, the city has been tearing down many of the area's old slum buildings - businesses and tenement apartments alike. As the buildings have fallen, so has the crime rate, Harris and police officials claim.

"Thirty per cent of the crime reduction along 14th Street came from the area being torn down," said veteran police officer George Bellinger as he patrolled the street recently and gazed at the empty lots now dominating the once busy commercial street.

The Career Criminal program, a joint project between the police department and the federal prosecutors to insure that repeated offenders receive maximum sentences, has also contributed to the area's lower crime problems, Rinaldi and Neslage said.

For those old 3rd Police District residents who had profited when the 14th Street corridor was its former rough-and-tumble self, homecoming after time spent in jail has been less than warm, police and neighbors say.

"I've seen the hardened criminal come back to see the neighborhood," Mildred Harris said. "But they don't linger because there is nothing here or not enough for them to hang around (for) . . . We don't have places that harbor criminals anymore."