The two previously unnamed senators blocking Richard C. Holbrooke's nomination as ambassador to the United Nations are Senate Majority Leader Trent Lott (R-Miss.) and Sen. Mitch McConnell (R-Ky.), congressional and administration sources said yesterday.

Lott and McConnell have put an "anonymous hold" on the Senate's confirmation of Holbrooke in an effort to pressure President Clinton to accept their candidate for a seat on the Federal Election Commission (FEC), the sources said.

Clinton has refused for months to nominate Bradley A. Smith, an associate professor at Capital University Law School in Columbus, Ohio, as one of three Republican members of the commission because Smith has been sharply critical of both Clinton and campaign finance reform.

By tradition, any member of the Senate can hold up a nomination. But the practice of blocking nominations anonymously, as a bargaining chip in unrelated matters, has come under growing criticism. After years of arguing about the practice, Republican and Democratic leaders agreed this year to do away with it.

The agreement, however, contains a loophole. Senators placing a hold must report it in writing to their party leader, but the leader is not required to make their names or reasons public. And there is no provision for disclosure when the hold is placed by the leader himself, as in Lott's case.

Last Wednesday, after the Senate Foreign Relations Committee approved Holbrooke's nomination, John Czwartacki, spokesman for Lott, told reporters that two or more senators had put "irreconcilable holds" on the nomination.

Sen. Charles E. Grassley (R-Iowa) announced in the Senate on Thursday that he was one of the three. He said he was delaying Holbrooke's confirmation in a dispute over the treatment of Linda Shenwick, a former employee of the U.S. mission to the United Nations. The State Department says it reassigned Shenwick because of unsatisfactory job performance; she contends that the move was retaliation for her calling attention to waste and mismanagement at the United Nations.

Lott told reporters on Friday that he thought the Senate eventually would approve the nomination of Holbrooke, an investment banker and former U.S. ambassador who negotiated the 1995 accord that ended the war in Bosnia. But without mentioning himself or McConnell, Lott said that the other anonymous senators' problems would have to be worked out first.

The White House has yet to be notified that Holbrooke's nomination is tied to Smith's appointment to the FEC. But presidential aides have been told that Lott has a strong interest in the Ohio law professor, sources said.

Smith would replace Republican Lee Ann Elliot, whose term expired in May, as one of three GOP members on the six-member FEC. In a telephone interview yesterday, Smith said he was recruited for the job last fall by McConnell. He added that he knows nothing about the latest maneuvering. "On hearsay," he said, he had been told that the White House objected to him because of a letter to the editor he wrote before the 1996 presidential election.

In that October 1996 letter to the Columbus Dispatch, Smith wrote that the series of "resignations, indictments and convictions" resulting from Kenneth W. Starr's investigation of the Clinton presidency "suggests that this may be the most corrupt White House in American history."

In an October 1996 article in the Wall Street Journal, Smith also called on GOP presidential nominee Robert J. Dole to "go negative" against Clinton. He wrote that Clinton's own 1992 campaign "was largely negative," that the president was vulnerable because top aides "have resigned in disgrace, been indicted or convicted," and that his administration was "guilty of gross negligence or worse in the handling of the Travel Office firings and the FBI files."

On the subject of campaign reform, Smith wrote in another Wall Street Journal opinion piece in 1995 that legislation proposed by Sens. John McCain (R-Ariz.) and Russell Feingold (D-Wis.) to reform campaign spending was based on "several erroneous assumptions about the effects of money in politics and would have detrimental effects on political equality and electoral competition."

Staff writer Helen Dewar contributed to this report.

CAPTION: Richard C. Holbrooke's nomination as ambassador to the United Nations is being held up to pressure President Clinton on other personnel issues.