Rockwell International and the United Auto Workers are preparing a plan to provide jobs for unemployed auto workers if Rockwell wins the tough competition to build a multi-billion-dollar long-range bomber for the Air Force.

Douglas A. Fraser, president of the UAW, said the union and Rockwell have agreed in principle that jobless auto workers who are permanently laid off should receive favored consideration if constgruction of Rockwell's proposed B1 bomber is approved. More than 10,000 auto workers eventually could be hired and retrained in aircraft assembly if the plan goes into effect, according to the UAW.

Rockwell, concerned about a possile deluge of job applications, cautioned that final arrangements with the UAW haven't been made.

More importantly, Rockwell doesn't know whether it will be able to build the B1, noted Jerry Syverson, head of Rockwell's Washington office.

It is one of two candidates under consideration by the administration as a long-range bomber capable of carrying nuclear cruise missiles to replace the Air Force's aged B52. General Dynamics Corp. is pushing equally hard for a contract to build a stretched version of its FB111 fighter-bomber.

General Dynamics would do the FB111 work at its Ft. Worth, Tex., plant, which strengthens its appeal to Sen. John Tower (R-Tex.), chairman of the Senate Armed Services Committee.

The Air Forces estimates that 180 of the FB111 bombers could be produced for $9 billion by 1984. A modified B1 bomber would be more expensive -- 100 could be built for between $17 billion and $22 billion, the Air Force estimates, and it would take more time to complete. However, B1 advocates contend it would be more effective against Soviet air defenses.

The Reagan administration's third option is to concentrate its bomber funds on perfecting a Stealth bomber capable of hiding from enemy radar.

Rockwell -- which now has 8,000 employes working on design of the B1 at its El Segundo, Calif., plant -- would hire additional workers for its Columbus, Ohio, and Tulsa, Okla, plants. The UAW is one of the major unions at Rockwell but not at General Dynamics.

If the administration does approve large-scale development of a modified B1, some 14,000 additional engineers, technicians, and construction and production workers would be hired between now and 1985, Syverson said. There also would be a large employment increase among the 3,000 subcontractors that would supply parts for the 1, he added.

No decision on the bomber choice is expected until June at the earliest.

Meantime, there isn't much else to offer the 180,000-plus auto workers now on indefinite layoff, Fraser said Wednesday.

"The worry and frustration has now become despair," he said in a speech to a Chamber of Commerce audience. Some will be rehired if the American auto market rebounds this year. But he said that another sales boom like that in 1978-79 doesn't appear likely because of the increasing automation of modern plants and changing buying patterns by consumers, who seem to be trading cars in at a slower rate.

Fraser and the UAW have been pressing Japanese automakers to build manufacturing and parts plants in the United States "to create jobs where their sales are," said Fraser. "That is the long-term solution."

The Labor Department estimates that 188,000 laid-off auto workers are receiving special unemployment aid under the Trade Adjustment Assistance program. It provides an additional 26 weeks of unemployment aid at a considerably higher level than state unemployment benefits.

The trade benefits ran out last year for 103,000 auto workers.