Yale University is moving ahead with a plan to build two new residential colleges, an expansion whose price tag has been estimated at $600 million, the university president, Richard Levin, said yesterday.

In a statement announcing his support for the idea, Mr. Levin said an expansion would ease an admissions process that has become dramatically tougher. The two new colleges would increase Yale’s total undergraduate population by 13%, or as many as 700 students, and would be completed by the fall of 2013, Mr. Levin said.

“Today, we have a long queue of highly qualified applicants who would collectively allow Yale to make an even greater contribution to society if more could be educated here,” Mr. Levin said.

Mr. Levin said previous cost estimates of $600 million are not final. Before requesting approval from the university’s overseers, he said he is asking finance officials to prepare a capital budget outlining the cost of building the dorms.

Right now Yale has 12 residential colleges, each of which has its own dining hall, dorms, and meeting spaces. The plan would add two more colleges of roughly equal size; Mr. Levin estimated each college would be about 235,000 square feet.

Harvard University has also been planning an expansion that would be the largest in its history. Championed by a former Harvard president, Lawrence Summers, as a way to increase the size of the college, the expansion would build four new undergraduate dorms and a large science complex across the river from the Cambridge campus, in the town of the Allston.