Colleges may deny admission to applicants who are living in the United States illegally, a federal judge ruled this week.

In dismissing part of a lawsuit that challenges the policies of seven public colleges and universities in Virginia, Judge T.S. Ellis III of the U.S. District Court in Alexandria said that states and their institutions do not overstep their authority or violate the rights of illegal immigrants under the U.S. Constitution by preventing them from enrolling.

However, the admissions policies could still be ruled unconstitutional, the judge said, if the institutions fail to use federal standards for determining an applicant's immigration status. The plaintiffs claim that institutions have failed to follow appropriate standards, and the judge's decision, issued on Tuesday, allows that portion of the lawsuit to proceed.

Those challenging the admissions policies include an immigrant-rights group, Equal Access Education, and two individuals. One is a high-school senior who is living in Virginia illegally and wants to attend college in the state. The second is a recent graduate of a Virginia high school who is an immigrant with temporary legal status; he was rejected last year by George Mason University and Virginia Tech, two of the institutions named in the lawsuit.

The other institutions whose admissions policies were challenged in the lawsuit are the College of William and Mary, James Madison and Virginia Commonwealth Universities, the University of Virginia, and Northern Virginia Community College.

The lawsuit was prompted by a memorandum that Virginia's attorney general, Jerry W. Kilgore, a Republican, sent to the state's public colleges and universities in September 2002. In the memo, Mr. Kilgore strongly cautioned the institutions against admitting illegal immigrants and encouraged college officials to report individuals living in the United States illegally to federal authorities.

This week, Mr. Kilgore said he was pleased by the ruling.

"I continue to believe that it is not too much to ask that people obey the laws of our society before they take advantage of what our society has to offer," Mr. Kilgore said in a written statement. "I look forward to continuing to represent the colleges and universities as this lawsuit continues, and trust that our institutions will continue to follow all state and federal laws."

Virginia's General Assembly is debating a bill this month that would prohibit public colleges from admitting illegal immigrants, effectively writing Mr. Kilgore's legal advice into law. The House of Delegates has approved the legislation, which is now pending in the State Senate.

Meanwhile, lawyers for the plaintiffs in the lawsuit said that they are reviewing their options for responding to Judge Ellis's ruling. They argue that denying admission to illegal immigrants unfairly punishes many students whose parents brought them to the United States at a very young age and who are likely to remain in the country. Denying those students a higher education prevents them from pursuing long-held career dreams while also limiting their earning power and their ability to contribute to states' economies, said Tisha Tallman, regional counsel for the Mexican American Legal Defense and Educational Fund, which is representing the plaintiffs.

If the decision stands, "it will be very, very detrimental to a lot of individuals," Ms. Tallman said. "These individuals have been integrated into our culture and consider themselves Americans. They've been raised in our schools and they hold on to American values."

A 1982 decision by the U.S. Supreme Court, Plyer v. Doe, bars elementary and secondary schools from considering immigration status when a student is seeking to enroll. The ruling does not apply to colleges.