A group of Washington investors previously involved with the bankrupt Auto-Train Corp. disclosed yesterday they have formed a new railroad to carry passengers and automobiles between Washington and Florida.

The Virginia and Florida Railroad Co. Inc. will "revive the Auto-Train concept" but will not necessarily take over the operations of Auto-Train, said Robert Ferneau, a spokesman for the new firm.

Investors in the Virginia and Florida railroad include the same people who last year loaned money to Auto-Train in an unsuccessful effort to keep that company going, Ferneau said.

Earlier the group had indicated it planned to submit a proposal to the federal bankruptcy court to reorganize Auto-Train Corp. and lead it out of bankruptcy.

But the investors now think it may be easier and cheaper to start a new railroad than to untangle the knotty financial affairs of Auto-Train and settle its millions of dollars of debts, the spokesman said.

Named president of the new railroad was William H. Moore, former bankruptcy trustee and later president of the Penn Central Railroad.

The Virginia and Florida hopes to have its auto-train service running by October, Moore said. "Negotiations are proceeding for acquisition of trackage rights, necessary operating equipment, locomotives and terminal facilities," he added.

The new line will try to acquire Auto-Train's terminals in suburban Lorton and Sanford, Fla., but will seek to replace Auto-Train's aging passenger cars and engines with more modern equipment.

A former Auto-Train passenger service manager, Obie Moore, also has been hired by the new group. The group previously was headed by G. William Middendorf, president of Financial General Bankshares Inc. Middendorf recently was appointed by President Reagan to be ambassador to the Organization of American States and is no longer active in the railroad effort.

Another group represented by former Auto-Train vice president Richard Tolbert also has expressed interest in reviving the railroad but so far has made no public announcement of its plans.

Court-appointed bankruptcy trustee Murray Drabkin recently received permission from the court to dispose of Auto-Train's assets. Drabkin ran the railroad after it filed for bankruptcy last fall. Earlier this year he said the company had run out of cash and received permission from the court to halt the service.

A local group in Seminole County, Fla., has approached Drabkin about acquiring Auto-Train's shop facilities there and selling repair services to other railroads.