The House Permanent Select Committee on Intelligence yesterday defied the Reagan administrtion and voted along party lines to stop financing and to prohibit by law any U.S. involvement with guerilla forces fighting the leftist government of Nicaragua.

The vote of nine Democrats against five Republicans followed five hours of closed committee deliberations and a last-minute warning from CIA Director William J. Casey that forcing the CIA to stop supporting the guerrillas inside Nicaragua could lead to a "bloodbath."

Republican and Democratic committee members said later that Casey offered no evidence to support his warning. Rep. Wyche Fowler Jr. (D-Ga.), chairman of the panel's oversight subcommittee, said the committee took great care to give the administration time to provide for an "orderly disengagement" from about 3,000 to 4,000 guerrillas currently making hit-and-run raids against targets inside Nicaragua.

At a reception for the diplomatic corps last night, Reagan told reporters: "What we're doing is perfectly proper. We'll keep right on fighting. If they [the committee members] want to be irresponsible that's their business."

As introduced last week, the bill would have cut off funds for the CIA operation 45 days after passage of the legislation.

But it was amended yesterday to substitute a period slightly longer than 45 days, which would remain secret to prevent the guerrillas from being routed by Nicaraguan government forces.

The legislation would amend the 1983 budget bill "to prohibit United States support for military or paramilitary operations in Nicaragua and to authorize assistance to be openly provided to governments of countries in Central America, to interdict the supply to military equipment from Nicaragua and Cuba to individuals, groups, organizations, or movements seeking to overthrow governments of countries in Central America."

Young said enactment of the legislation would bring about "an exciting day for the Sandinistas in Nicaragua . . . and would give the Sandinista-backed insurgency in El Salvador a real morale boost."

"No Reagan administration offer of compromise surfaced during the five-hour committee session yesterday, although Young said Casey brought a "complete rewrite" of the Boland bill ready for introduction. The rewrite would allow the covert operations to continue, Young said.

Casey and Thomas O. Enders, assistant secretary of state for inter-American affairs, spent most of the morning with the committee and then caucused with its five Republicans during a luncheon recess.

During the recess, Young said, Casey and Enders decided not to try to substitute the administration rewrite of the Boland bill in the committee. Instead, Young said, they agreed to back his amendment, which would have allowed the covert operations to continue until "after a verifiable agreement is reached that the government of Nicaragua ceases activities to provide arms, training, command and control facilities or logistical support to military or paramilitary operations in or against any government in Central America."

One Democratic member said Enders was challenged in the closed committee session for having "no discernable policy for negotiations" to resolve differences with the Nicaraguan government. "One was left with the inescapable conclusion that they are seeking a military solution," the committee Democrat said.

One member said Casey warned the committee that "disengagement would be very difficult and dangerous and could lead to substantial casualties" among the anti-Sandanista forces.

But on close questioning, Casey apparently acknowledged that the Sandinistas have not attempted to bring their full military forces to bear on the U.S.-backed guerrillas and that there is no reason to expect they would if those forces began a withdrawal.

Young said he agrees that the "potential is there" for a bloodbath, but that Nicaraguan actions to date do not suggest one. "The Sandinistas could easily give them five days to get out of town," Young said.

The intention, according to Democratic committee members, is to provide El Salvador and Honduras with open assistance to stop any illicit flow of arms to leftist insurgents from Nicaragua while ending covert support for the guerrilla campaign against Nicaragua's Sandinista government.

The CIA has claimed the covert operation is succeeding. But critics said it is driving the Nicaraguan government toward greater repression and is harming U.S. credibility in the region.

The Senate Select Committee on Intelligence met for two hours yesterday afternoon to consider similar legislation, but recessed without taking action. Committee sources said that the administration appears to have enough support there to defeat the measure, which could leave Congress split over one of the administration's most sensitive foreign policy ventures.

After the House committee vote, chairman Edward P. Boland (D-Mass.) said, "What this committee has done, what the majority of the members believed had to be done, was to cut off covert operations in Nicaragua."

Boland said CIA pressure on the Sandinista regime to stop supporting the leftist insurgency in El Salvador had become "counterproductive" and against the best interests of the United States.

The legislation, sponsored by Boland and House Foreign Affairs Committee Chairman Clement J. Zablocki (D-Wis.), now will be referred to Zablocki's panel, which would have jurisdiction over the "overt" arms interdiction assistance provided in the bill, amounting to $30 million in this budget year and $50 million in the budget year beginning Oct. 1.

Boland said he expects quick action in the Foreign Affairs Committee, which would put the bill next week on the House floor, where a secret session has been authorized by House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.). At a meeting with reporters yesterday, O'Neill endorsed the Boland-Zablocki proposal.

In reporting the bill, the House intelligence committee rejected an amendment by Rep. C.W. (BIll) Young (R-Fla.) that would cut off covert funding for the anti-Sandinista guerrillas only after it could be determined that the Sandinistas have stopped supporting the rebels fighting the Salvadoran government.