The Massachusetts Bay Transportation Authority is taking another stab at solving one of its perennial problems: finding a new site for the car storage facilities now located across from Eliot House where the Kennedy Memorial Library will someday stand.

This time, the MBTA is trying to relocate the so-called "car barns" on a site in the Penn Central yards in South Boston. In preliminary talks with the Penn Central, MBTA officials have proposed trading other land the MBTA owns in the area for the 12-acre site where they want to put the car barns.

An MBTA spokesman said Friday that the outlook was encouraging: "It looks pretty good that the MBTA will be able to acquire the land. It looks as though we have finally found a home."

Several previous attempts to relocate the car barns ended in failure.

The failure of the relocation attempts has set back the construction of the Kennedy Library by several years, according to competent observers.

The MBTA had originally wanted to put the car barns in Codman Square in Dorchester, but legislative pressure blocked that attempt.

Then, last year, they tried for a site in Mattapan Square, but the Town of Milton went to court to fight that attempt. Though the MBTA won an initial court decision, the Town appealed the decision to the Supreme Judicial Court of the Commonwealth. The appeal is still pending.

Reviewing the history of the relocation attempts, the MBTA's "master plan" released in February noted that the Mattapan Square site had not been the authority's first choice, suggested the Penn Central site, and concluded, "the entire matter is now under review."

A few days after the master plan was released, a report leaked out that the MBTA was considering a tract of land in South Braintree. Local officials there protested, and it now appears that the South Braintree site has fallen out of favor with the MBTA, leaving the Penn Central yards as the prime prospect for the car barns.