Beth Israel Deaconess Medical Center and Milton Hospital yesterday announced plans to merge in six months. The change reflects a trend toward consolidation among hospitals, as they adjust to federal health laws designed to reward large, efficient health care systems. The two hospitals have had a relationship for several years. Doctors from Beth Israel Deaconess staff the Milton emergency department. The Boston hospital, which brought in $1.24 billion in revenue in 2008, the most recent year for which tax forms are available, provides a streamlined transfer process for Milton patients having heart attacks. The two hospitals also partner on clinical programs, including geriatrics. Milton, which reported $61.9 million in 2008 revenue, will keep control of strategic planning and its own board of trustees, which already includes members from Beth Israel Deaconess. The larger hospital will have oversight of Milton's operations and finances.