Fort Dix. N.J. where millions of Americans made the bumpy passage from civilian to soldier, will be phased out as a training base starting in October under a Pentagon plan to be made public today.

The plan part of a massive reorganization of about 85 military installations that the Defence Department says will save $250 million a year, envisions keeping Fort Dix under Army control for unspecified purposes.

However, memebers of the New Jersey congressional delegation vowed yesterday to fight the Pentagon's decision, which they noted will take budgetary authority.

"they still hasm't reached the White House level," said Rep. Edwin N. Forsythe (R.n.j.), whose district encompasses the threatened base. "This leaves the whole Northeast without a single training area. This had to be a political decision, rather than one that was just a matter of straight old dollars and cents."

The New Jersey delegation was briefed on the closing yesterday by Alan J. Gibbs, assistant secretary of the Army for installations.

Although the Army declined to comment on the decision, and Army study recommending the "disestabilishment" of Fort Dix has been circulating widely. The Army had been trying to close the base for a number of years. Congress blocked one attempt and President Ford later opposed the closing.

The new study argues that closing Fort Dix would save $20 million immediately and an additional $14 million annually.

The Army says that consolidation of its training facilities is justified by a sharp reduction of recruits since the rndof the Vietnam war. The Army is now taking about 200,000 recruits a year compared with nearly 500,000 a year in 1968.

However, Rep. James. J. Florio (Dn.j.) yesterday challenged claims of large savings resulting from the ending of training operations at Fort Dix.

He said the Army indicated that it will cost $63 million to construct training facilities elsewhere to replace those at Fort Dix. Congressional aides asserted that the Army has spent $79 million on new construction at Fort Dix since 1965.

The Army study reportedly weighed the advantages of closing eigher Fort Dix or Fort Jackson, S.C., and decided to maintain and expand training operations at the southern facility.

Sen. Ernest F. Hollings (D.s.c.) announced Tuesday that he had learned from the White House that much of the Fort Dix program would be switched to Fort Jackson.

A Hollings aide said yesterday, "We have the most efficient training center in the country, and we feel the right decision was made."

Congressional sources sait that 1,281 military and civillian jobs at Fort Dix will be transferred or dropped. About 68200 recruits train at Fort Dix at one time. Some military and civilian staff will stay there, but the economic impact of the planned, phaseout still would be heavy. Under the Pentagon's plan, all training operations at Fort Dix would end in 1982.

The combined payroll, services and supplies for Fort Dix have been running around $148 million a year, and this money is important for the local economy, which already has felt the impact of curtailed Army recruitment.

Millions of Americans have known Fort Dix in this century. After World War I, as Camp Dix, it was where returning servicemen were separated from the Army.

It was a training center for Civilian Conservation Corps members in the New Deal. With the start of the draft and World war Ii, Fort Dix became a major infantry training base and staging area for troop movements overseas, a role it also had during the Korean War.

Today, Fort Dix still trains cooks and vehicle maintenance specialists in addition to infantrymen, but most advanced training has moved elsewhere