The House approved $3.5 million in new "humanitarian" aid to the Nicaraguan contras yesterday, and House Speaker Jim Wright (D-Tex.) said he expects it to be the last U.S. aid ever sent to the rebels.

The money was part of a stopgap spending bill to keep the government running after the current fiscal year ends Wednesday. The measure, approved 270 to 138 after little debate, was sent to the Senate, where it is not expected to encounter major opposition.

The contra aid had been worked out in a bipartisan agreement between Wright and House Minority Leader Robert H. Michel (R-Ill.).

The $3.5 million represents the proportion of this year's $100 million in contra aid money that has been used for food, medical supplies and uniforms and would be needed to sustain the rebels into November in their battle against the leftist Sandinista government in Managua.

Asked whether he believed the money would be the last U.S. aid to flow to the rebels, Wright said, "Yes, unless some drastic change were to occur in the situation in Central America. The evidence indicates to me reason to be optimistic -- still guardedly, but less guardedly than before."

The Reagan administration has signaled its intention to ask for $270 million in new military aid for the contras over 18 months if a regional peace plan fails.

During House debate on the aid, Rep. David E. Bonior (D-Mich.) said the money is merely a means to help bring an orderly end to hostilities by letting the contras make the transition to civilian life.

"Passage of this legislation should not be taken as a sign of support for the contras or for this administration's policy in Central America," Bonior said. "The policy, in my mind and the mind of most members of this party, has been a failure."

The spending bill, known as a continuing resolution, was approved after lawmakers added the contra aid and sent it to the Senate. The bill also has White House support.

Without the resolution, government agencies will be without spending authority and forced to shut down on Oct. 1, the beginning of fiscal 1988. The resolution would let them operate at fiscal 1987 spending levels for an extra 41 days.

Congress is months behind schedule in approving its appropriations bills. The House has passed 10, but none have cleared the Senate.

House Appropriations Committee Chairman Jamie L. Whitten (D-Miss.) said he was hoping the Senate would move forward with its bills and the two chambers would soon get legislation to the president.

Wright, meanwhile, announced that other budget legislation was also being delayed. A deficit-reduction package including a tax increase had been scheduled for action before Congress' summer recess, but was postponed until next week. Wright said the deadline would be extended again, until the middle of next month.

Democratic leaders have said that tax increases are needed to reduce the deficit. But they have not agreed on which taxes should be increased, and President Reagan has threatened a veto.