The D.C. police department underwent a major reshuffling yesterday, including the promotions of 1st District Commander Isaac Fulwood Jr. to assistant chief for field operations, the No. 2 post, and Inspector Joyce F. Leland to deputy chief in command of the 7th District -- the highest rank ever achieved by a woman member of the force.

The promotion of Fulwood, 44, a controversial 20-year veteran and a favorite of Mayor Marion Barry, was viewed by some as a move to groom him to succeed Police Chief Maurice T. Turner.

Fulwood, who will replace Marty Tapscott as head of field operations, was cleared in two department investigations into allegations that he underreported major crime while he commanded the 6th District and that he participated in illegal gambling at a carnival in April 1983.

Tapscott, who was reassigned to head the technical services bureau, complained angrily yesterday that he had not been given any warning, even after he had inquired about rumors of change, and that his abrupt transfer had been handled by Turner unprofessionally and "without integrity."

"I've worked hard for him for 3 1/2 years and crime has gone down for 3 1/2 years," said Tapscott, who will retain the title of assistant chief but in effect is now third or fourth in command. "That's the reward that you get for working hard."

In a somewhat unusual move, Barry preempted Turner in announcing the promotions and reassignment of 35 officers yesterday, prompting speculation that the mayor may have forced Turner to replace Tapscott with Fulwood.

Max J. Krupo, 37, a 15-year veteran who heads the data-processing division, was promoted to replace Fulwood as a deputy chief in charge of the 1st District.

In an interview late yesterday, Turner said that he had recommended the changes to Barry last month, before the mayor left on a three-week trip to Africa, including the promotion of Fulwood. However, sources within the police department insisted that Turner had acted on the mayor's request.

"Field operations is a very demanding job," Turner said. "It's a job where you have to continually come up with new innovations, new ideas, new thoughts.

"Chief Tapscott has been in there 3 1/2 years. He's been a good police officer . . . . There's been no diminishing in his power and authority. He's still an assistant chief."

Asked whether he had been concerned at all about promoting Fulwood in light of the two investigations of his conduct, Turner said, "If I thought there was a cloud, he wouldn't have been recommended for promotion."

"I am looking forward to achieve the goals that Chief Turner has set to reduce crime and make the city the safest place where residents can work and live in comfort and safety," Fulwood said.

Fulwood said that he has not received any special favors from the mayor. "The mayor has never committed himself to me," he said. "All the promotions that I have received have been recommendations of the chief indicating to me that he is satisfied with my work performance and my leadership style."

In a statement issued by the mayor's office, Barry said: "Each of those being promoted has shown both skill in managing a modern major urban law enforcement unit and dedication to protecting our citizens. Deputy Chief Leland's promotion is another example of our leadership to appointing women to the full range of management positions throughout the government."

Leland, 43, a 19-year veteran of the force, previously served as the department's equal employment opportunity officer. She has become the first woman in the department's 123-year history to achieve the rank of deputy chief and to be placed in charge of a district. The 7th District, which covers Southeast Washington, is considered by many to be among the toughest assignments.

"I feel I can contribute to the department and all female officers to show that they can make it on their own," Leland said yesterday. "It has not been easy. I have had to overcome a lot of prejudice, but it has made me a much stronger person."

Promoted to inspectors were James G. Brunzos, 40, Willie M. Doster, 42, and Sammie D. Morrison, 45. Brunzos, a former commander of the traffic division, and Doster, former head of the promotional process office, will be night supervisors. Morrison will remain in charge of the office of finance and management. Claude J. Beheler and David P. Baker were promoted to captains.

Inspector Gary L. Abrecht was reassigned from night supervisor to the equal employment opportunity office, while Inspector Kenneth L. Hutson was transferred from night supervisor to the data-processing division. Seven sergeants were promoted to lieutenant and 20 officers promoted to sergeant.