After 30 years of effort, Massachusetts is set to embark on a federal project to deepen Boston Harbor, with the announcement Monday of a $27 million contract award to Great Lakes Dredge & Dock Co.

Massachusetts Port Authority officials say the removal of nearly 3 million cubic yards of material is expected to start in late June, giving Boston badly needed access for deeper-draft container ships and oil tankers. The work may take up to 18 months but could be done in as little as a year, said Deborah Hadden, Massport's manager of maritime environmental affairs.The project comes at a time when major carriers are shopping for an East Coast load center as an alternative to New York-New Jersey, where dredging has been stalled for years due to environmental concerns.

''If you build it, they might come. If you don't build it, they definitely won't come,'' said Peter Jackson, the project's manager at the U.S. Army Corps of Engineers.

Environmental problems have also dogged Boston through the long history of its attempts to deepen harbor channels, tributaries and berths since Congress first passed a resolution to examine the project in 1968. As recently as 1992, the corps and Massport suffered a major setback when they were barred from using a longtime offshore dump site for contaminated silt.

But officials came back with an innovative plan that won over environmental groups. The design calls for digging a series of up to 50 football-field-sized ''cells'' or pits in the actual path of the dredging. The cells, which will be about 20 feet deeper, will be used to collect all the contaminated silt which has settled on the harbor floor.

Cells will be capped with clean sand and gravel, isolating the nearly 900,000 cubic yards of silt. Only the 1.8 million yards of clay and other clean material from underneath will be taken to the offshore disposal site.

The harbor's Mystic River channel will be deepened from 35 feet to 40. The Chelsea River, which is home to oil terminals, will go from 35 to 38 feet. The ''reserved channel'' near Conley Terminal in South Boston will be dredged to 40 feet. Harbor approaches and anchorages will be realigned and enlarged.

The work will ease carriers' perennial problem in Boston of having to wait for the tides in order to dock. Some have bypassed the port to meet schedules in New York. The last maintenance dredging in the harbor was in 1983.

The project, once estimated to cost nearly $60 million, is also benefiting from the low $27 million bid by Great Lakes of Oak Brook, Ill., although an additional $5 million will be spent to dredge 10 berths. Massport and the state are expected to share costs of some $17 million.