Democratic leaders of the House and Senate last night supported the U.S. military action against Libya, but House Foreign Affairs Committee Chairman Dante B. Fascell (D-Fla.) suggested President Reagan may have violated the War Powers Act by failing to consult with Congress in advance.

After being briefed at the White House, congressional leaders of both parties either maintained silence or cautiously backed the president's handling of the military action. A few Democrats criticized the action, accusing the president of trying to provoke a confrontation with Libyan leader Muammar Qaddafi.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said Reagan was "on the right course." And Senate Minority Leader Robert C. Byrd (D-W.Va.) agreed that the U.S. should respond militarily when fired upon in international waters.

"Based upon the briefing given me at the White House, the American planes attacked by Libya today were on a peaceful mission in international waters," said O'Neill in a prepared statement.

"The administration's handling of this matter is on the right course," the speaker added. "Its actions in protecting America's armed forces in international waters is justified."

"If we're going to get fired on in international waters, we will fire back," Byrd was quoted by an aide as saying.

O'Neill did not mention the War Powers Act. And Byrd said he heard nothing in the White House briefing to merit invocation of the post-Vietnam law, which imposes limits on presidential deployment of combat troops without congressional approval.

"I don't see anything from what we were told that it the U.S. military encounter would involve the War Powers Act," Byrd said.

However, Fascell said in a letter late yesterday to Reagan that he thinks that the administration "failed to adequately satisfy requirements" of the War Powers Act that mandate consultations with Congress before U.S. combat troops are involved in hostilities.

"As demonstrated by today's reported attack, these deployments constituted from the outset a situation where imminent involvement in hostilities was a distinct possibility clearly indicated by the circumstances even prior to today's development. Under the circumstances, prior consultation with Congress was required under the War Powers Act. In view of these circumstances, I respectfully urge you to comply fully with the provisions . . . before the situation evolves further."

The War Powers Act of 1973 permits the president to send combat troops into battle or situations where "imminent hostilities are likely" for no more than 90 days without approval of Congress. In a statement issued along with release of the letter, Fascell called on Reagan to issue a report that would trigger requirements of the law.

In other congressional response to the crisis, House Minority Leader Robert H. Michel (R-Ill.) said the information he received indicated that Libya engaged in an "act of provocation that warranted our response." Senate President Pro Tempore Strom Thurmond (R-S.C.) said the United States had the "right and duty" to fight back.

Other views ranged from an assessment by Sen. Warren B. Rudman (R-N.H.) that Qaddafi "ought to be thankful that the U.S. Navy was restrained" to an assertion by Rep. Ronald V. Dellums (D-Calif.), a ranking member of the Armed Services Committee, that Reagan played "a deadly game of chicken, callously risking the lives of thousands of U.S. military personnel."

Sen. Jim Sasser (D-Tenn.) said "there is no doubt that the U.S. exercises were provocative" and suggested that an international response would have been more appropriate. In any case, he said, the administration "has made its point . . . and I believe now that our naval forces should be withdrawn from the waters."

Sen. Alan Cranston (D-Calif.) said the incident strengthened his resolve to block a proposed arms sale to "Mr. Qaddafi's friends, the Saudis." Sen. John Heinz (R-Pa.) said the U.S. retaliation could lead to a terrorist response from Libya but could also be "necessary to draw the line with the sort of dangerous, violent misbehavior practiced by Qaddafi's Libya."