Mr. Rostenkowski has been under scrutiny since last year, when his office records were subpoenaed in an inquiry into whether someone in his office used his expense account fraudulently to obtain cash from the post office. Since then, some of his aides have testified to a grand jury and investigators have examined his use of campaign funds. Denies Any Connection

In announcing her order at her first news conference as Attorney General, Ms. Reno denied there was any connection between her action and the Rostenkowski case and said Mr. Stephens had been treated like other United States Attorneys."

Ms. Reno said United States Attorneys "are absolutely integral to the whole success of the Department of Justice," and her aides said today that she did not intend to immediately remove any whose presence was required to complete an investigation.

One official suggested that even Mr. Stephens might be asked to stay on until a successor is named, saying Ms. Reno had made no decisions about who she may choose on an interim basis.

All 93 United States Attorneys knew they would be asked to step down, since all are Republican holdovers, and 16 have resigned so far. But the process generally takes much longer and had usually been carried out without the involvement of the Attorney General. Battles of the Past

Ms. Reno is under pressure to assert her control over appointments at the Justice Department. She was Mr. Clinton's third choice for Attorney General and arrived after most of the department's senior positions were already filled by the White House.

The comments of Ms. Reno and Mr. Stephens evoked the pitched battles of the past, when independent United States Attorneys resisted removal by new administrations.