The chairman of the influential Senate D.C. appropriations subcommittee, an an unusual move, has urged Mayor Marion Barry to appoint assistant police chief Charles E. Rinaldi, generally considered a long-shot candidate for the job, as the District's new chief of police.

In a letter offering his "strong endorsement" of Rinaldi, Sen. Alfonse D'Amato (R-N.Y.) wrote, "It is apparent that support for him is very broad, including the support of various community, civic and business organizations. His professional credentials are impeccable and his long experience in the department would help to insure its efficient operation."

"I am confident," the letter concludes, "this appointment would reflect favorably upon both yourself and the District of Columbia."

The letter obliquely raises the issue of race. Rinaldid is white, and conventional political wisdom has it that Barry would be damaged politically if he were to name a white as police chief. Chief Burtell M. Jefferson, who is scheduled to retire June 30, is the city's first black police chief.

D'Amato's April 21 letter also revives the question of Capitol Hill influence in city affairs. Rarely since the city abandoned the three-commissioner form of government in 1967 have members of the congressional committees that oversee the District been so bold in letting their preferences for police chief be known. D'Amato's subcommittee oversees congressional budget appropriations for the financially strapped city government.

Police sources have indicated that while Barry apparently has not made a final decision, particularly on a way to shuffle the department's top officials immediately beneath the level of chief, the apparent front-runner for chief is assistant chief Maurice T. Turner, a 24-year veteran who now serves in the department's number-two position as head of field operations. Rinaldi has been considered a top contender to replace Turner if Turner become chief.

In his letter to the mayor, D'Amato wrote, "It is my understanding that you are very close to choosing a new chief of police for the District of Columbia . . . Several members of the District of Columbia police department have contacted my in support of assistant chief Rinaldi . . . I do hope you will favorably consider elevating assistant chief Rinaldi to the position of chief of polict."

D'Amato was out of town and could not be reached for comment yesterday.

Alan Grip, the mayor's spokesman, said Barry sent D'Amato a responding letter in which "he expressed his appreciation for the senator's concern." Barry wrote to the senator "that he would choose the most competent person as chief," Grip said.

Since March 26, when Jefferson's plans to retire were announced, Barry has interviewed the department's top officers and met with business and civic leaders as part of his search for a successor.

Besides Turner, 45, and Rinaldi, 51, the leading contenders for the job are assistant chief Marty M. Tapscott, 44, who heads the administrative services bureau, and deputy chief Issac Fulwood, 40, the department's top budget official. Fulwood and Tapscott are black.

Insiders had hoped that the new chief would be named within two weeks of the March 26 announcement of Jefferson's plans to retire, to minimize the politicking to fill the vacancy. The day after the announcement, City Administrator Elijah B. Rogers immediately began preliminary interviews with the department's four assistant chiefs and 11 deputy chiefs, and, according to sources, urged the mayor to act quickly.

Over the past two weeks, Barry also has interviewed the top department officials. On Tuesday, he discussed the selection of the new police chief with former police chiefs Jerry Wilson and Maurice Cullinane and developer and parking lot owner Leonard B. Doggett Jr. The mayor met Wednesday with representative of the International Brotherhood of Police Officers Local 442, which represents the rank-and-file officers.