The pending Reagan administration decision on whether to put all its chips on one new bomber or try to develop two at once has generated a bitter fight inside the Air Force, with Chief of Staff Gen. Lew Allen and his Washington headquarteres staff pitted openly against retiring Strategic Air Commander Gen. Richard Ellis and his staff in Omaha.

The disagreements between the generals have gone beyond the bomber issue into such areas as the type of warhead wanted for the new MX missile and who should replace Ellis.

One officer says the men's personalities are so different that they were bound to clash. Allen is the academic; Ellis the gruff, outspoken general on the Curtis LeMay model.

Allen has been lobbying strongly for the two-bomber approach, under which the Air Force would move ahead simultaneously on a new B1 bomber and a so-called Stealth bomber able to evade detection by radar. Ellis has been pushing for what is now called the one-bomber idea, which is to modernize and make interim use of an existing bomber while moving ahead with Stealth.

Ellis, according to sources, recently asked Defense Secretary Caspar W. Weinberger to name his SAC deputy, Lt. Gen. Lloyd R. Leavitt Jr., as the next head of SAC. Like Ellis, Leavitt is considered outspoken and a hard-charger among Air Force generals.

Allen and his officers strongly opposed Leavitt, and pushed instead for Gen. Bennie Davis, chief of the Air Force Training Command. Like Allen, Davis is soft-spoken and less of an activist commander. More important in Allen's terms, Davis favors the B1/-Stealth, two-bomber approach.

Davis' name was sent to President Reagan more than a week ago, and the White House announced his appointment yesterday. Air Force sources said it appears that Leavitt, Ellis' protege, will retire before the end of the year.

Allen and Ellis have also been fighting over the next warhead for the MX intercontinental ballistic missile (ICBM). Allen believes the existing Mark 12A warhead, with its 340 kilotons of explosive power (more than 25 times as powerful as the Hiroshima bomb), would be good enough for the MX. Ellis wants a newer, bigger 500-kiloton warhead that is still being designed.

When a lobbyist for General Electric Co., which builds the Mark 12A, got the House Armed Services Committee to add $47.5 million for the warhead to the fiscal 1982 defense authorization bill, Air Force headquarters went along with the idea while Ellis argued to have it cut out.

The internal Air Force battling, however, has been at its most intense over the bomber issue. It got so heated in recent weeks that Weinberger's office ordered both sides to stop meeting on the Hill or calling members to get their views across.

Ellis opposed former president Jimmy Carter's decision to cancel the B1, saying that because the United States was becoming vulnerable to Soviet ICBMs, the best fix to the looming warhead gap was production of a stretch FB111 bomber.

When Regan was elected on a platform that criticized the B1 decision and called for "accelerated development and deployment of a new manned strategic penetrating bomber," Ellis proposed his FB111 idea as the interim answer while research went on for an advanced penetrating bomber along Stealth lines.

Allen and his staff, however, quickly moved toward immediate production of the B1 while continuing research on Stealth. Their notion was that any breakthroughs could be added to later B1 production models.

Ellis, however, critized that approach, telling questioners that he was afraid so much money would be spent on the B1 that the Air Force would never get to the Stealth bomber.

As both officers pressed their cases, it became clear there could be no reconciliation.

When the Air Force chief of staff's two-bomber decision went to Weinberger last month, he first learned that his SAC commander disagreed with that approach.

According to congressional sources, Weinberger's staff also found important differences over the likely cost figures and operational dates for the aircraft, involved.

For example, the Air Force, these sources said, told Weinberger that the Stealth aircraft could not be available until the early 1990s. Ellis reportedly had been saying that if the Pentagon dropped the B1 and focused on Stealth, it could have the first of the new bombers by 1988.

To sort out what was true, Weinberger last month called in the two manufacturing teams that are competing for the big Stealth development contract -- four of the nation's top six aircraft manufacturers.

Lockhead has designed a fighter-sized Stealth and has teamed with Rockwell to bring it into fruition.

Northrop also has worked on a Stealth design and has joined with Boeing on the project.