WASHINGTON — Advancing what could become a near-total rebuild of the U.S. nuclear weapons arsenal, the Air Force on Friday solicited industry proposals to build a new fleet of land-based nuclear missiles as well as replacements for its air-launched nuclear cruise missile force.

The two projects are part of a broader modernization of the nuclear arsenal expected to cost hundreds of billions of dollars over 30 years. The plans have broad support in Congress, although some, including Sen. John McCain, R-Ariz., have questioned the need to replace all three “legs” of the nuclear triad – the submarines, long-range bombers and land-based missiles that were developed by the Pentagon during the Cold War.

The Air Force operates two of the three legs the nuclear arsenal – the bombers and the Minuteman 3 intercontinental ballistic missiles, or ICBMs, that are ready for launching on short notice from underground silos in five states.

On Friday the Air Force asked that industry contractors submit proposals for a new-generation ICBM, and said it plans to award the first contracts next summer. It would replace the existing fleet of about 450 deployed Minuteman 3 ICBMs, starting in 2027. The estimated cost is $62.3 billion.

The Air Force quoted Gen. Robin Rand, who heads Air Force Global Strike Command, as saying the Minuteman 3, which was first deployed in 1970, will have “a difficult time surviving” air defenses foreseen for 2030 and beyond.

The Air Force also requested contractor proposals for a new-generation nuclear cruise missile to replace the existing AGM-86B cruise missile, which go back to the 1980s.

Critics of buying a new nuclear cruise missile include a former secretary of defense, William Perry, who has called on President Obama to scrap the project.