Washington — Sen. Edward M. Kennedy of Massachusetts, who suffered a seizure over the weekend, has received a diagnosis of a malignant brain tumor, the Associated Press reported this afternoon.

It is unclear when Senator Kennedy, a Democrat and major figure in higher-education policy making, will return to Congress and what effect his absence will have on efforts to reauthorize, or renew, the Higher Education Act, the main law governing federal student aid. As chairman of the Senate education committee, Mr. Kennedy is a key player in that process.

Lawmakers had hoped to complete work on a compromise measure before they leave town for the Memorial Day recess, at the end of this week. But with several issues still unresolved, and at least one senator threatening to put a hold on the bill, hopes of reaching that target had dimmed even before Mr. Kennedy was hospitalized over the weekend. This morning, the Senate passed a bill to extend the Higher Education Act for 30 days beyond the late-May expiration date. The House of Representatives is expected to pass the bill soon.

The senator’s grim diagnosis introduces yet more uncertainty into the reauthorization process. According to the AP, malignant gliomas — the type of tumor Senator Kennedy has — are typically treated with combinations of radiation and chemotherapy. Average survival rates range from less than a year to about five years, depending upon the aggressiveness of the cancer.

If the senator is unable to return to Congress for an extended period of time, several scenarios are possible. Lawmakers could delay further action on the bill until he returns, potentially putting off reauthorization for another year. Aides could press on with behind-the-scenes negotiations, with Mr. Kennedy casting a proxy vote when Congress convenes a formal conference committee. Sen. Christopher J. Dodd of Connecticut, the second most senior Democrat on the education committee, could manage the conference and floor debate in Senator Kennedy’s absence.

Which of those scenarios, if any, plays out will depend on Mr. Kennedy’s preferences, lobbyists and aides said today.

“I think it is reasonable to expect that Chairman Kennedy’s desire to either move or delay the conference agreement will be respected,” said Matt Owens, associate vice president for federal relations at the Association of American Universities.

While at least some delay is likely, lobbyists were optimistic that the reauthorization bill, which is five years overdue, would finally pass the Congress this year.

“This guy is so resilient and focused — he would come back for two weeks and say, ‘Let’s do something in between treatments,’” said Sarah A. Flanagan, vice president for government relations at the National Association of Independent Colleges and Universities. —Kelly Field