Frank C. Carlucci was confirmed by the Senate as secretary of defense yesterday, and he forced out the Pentagon's senior nuclear arms control official, a move that touched off reports Carlucci plans to dismiss other senior Defense officials.

The Senate's 91-to-1 vote came amid bipartisan predictions that the choice of Carlucci, 57, a career federal official, to succeed retiring Caspar W. Weinberger could ease friction between the Reagan administration and Congress on military and arms-control issues.

Sen. Jesse Helms (R-N.C.) cast the lone dissenting vote after an unusual debate in which the nominee of a Republican administration was touted mainly by Democrats.

But at the Pentagon, news that arms-control expert Frank J. Gaffney Jr. was being replaced by a Carlucci choice, strategic arms negotiator Ronald F. Lehman, touched off a wave of other reported ousters and uncertainty over the new secretary's top staff.

Pentagon press chief Fred S. Hoffman was among those reported to be leaving. Dan Howard, a White House deputy press secretary who worked as Carlucci's spokesman at the National Security Council, will succeed Hoffman.

But another senior official on the widely rumored departure list, Fred C. Ikle, undersecretary for policy, said he had spoken to Carlucci and that he is staying in his job for the foreseeable future.

Gaffney, Richard N. Perle's former deputy and anticipated successor, left his job last night expressing concern about the current drive to negotiate an arms pact with the Soviet Union under a summit deadline. Gaffney said he had written a resignation letter to President Reagan Thursday night saying the United States is "now in a very dangerous situation" in the drive to complete the intermediate-range nuclear forces (INF) treaty in time to be signed at the Dec. 8-10 summit meeting here with Soviet leader Mikhail Gorbachev.

Lehman, 41, is reported to be Gaffney's successor as assistant secretary of defense for international security policy, the top Pentagon arms control job.

Gaffney, 34, was nominated in April to succeed Perle, but the Senate never held a hearing on his nomination and showed no sign of moving toward confirmation. For the time being, Gaffney said, he will join the American Enterprise Institute, where Perle is a resident scholar.

Gaffney said Carlucci called him Thursday night to tell him he had made another choice for the top job and to ask Gaffney to stay on as a deputy. Gaffney said he was "somewhat relieved" to depart in view of his worries about last-minute INF treaty compromises.

He said that negotiating the final elements of the INF treaty under the deadline of the coming summit gives the Soviet Union "enormous leverage" on the final provisions to be decided.

He declined to identify provisions of the draft treaty that are the sources of his concern but said he had "expressed reservations" in recent weeks about some U.S. offers to the Soviets.

Gaffney conceded it is unlikely that the treaty talks will be slowed.

Meanwhile, U.S. negotiators in Geneva were to work through the weekend on the last unresolved issues on the INF treaty before the meetings there Monday and Tuesday by Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze.

In the Senate, Carlucci was praised by Democrat after Democrat for his service as a senior federal official.

"He has demonstrated he is well aware of the tough defense budget decisions that will be needed" and has shown a willingness to work with Congress on this and other issues, said Senate Armed Services Committee Chairman Sam Nunn (D-Ga.).

Sen. John W. Warner (R-Va.), ranking minority member of the committee, the only Republican to take the floor on Carlucci's behalf, noted Carlucci "raised a few eyebrows in this town with his frankness and candor" at the hearings. "I predict the working relationship between Mr. Carlucci and the Senate and perhaps the House will be the best working relationship in the history of that office."