Congress gave final approval yesterday to legislation designed to complete construction of the Federal Triangle, which was halted by the Great Depression. The bill authorizes a new International Cultural and Trade Center, which will be the biggest building in the District.

The $362 million center will provide office space for the Justice and State departments and three to four floors of shops and exhibits from every continent.

The center will be built by private developers on an L-shaped site abutting the District Building at 14th Street and Pennsylvania Avenue NW on what Sen. Daniel Patrick Moynihan (D-N.Y.) described as the home of a "parking lot of surpassing ugliness."

"This bill brings to triumphant completion a 25-year program that President Kennedy set in place to redevelop Pennsylvania Avenue," Moynihan said of his bill, which was passed unanimously by the House yesterday after Senate action Thursday and sent to President Reagan for his expected signature. "This has not been a business for the short-winded," Moynihan said.

"This building will be a spectacular building, consistent with the other buildings in the Federal Triangle," said Terence C. Golden, administrator of the General Services Administration. It will save money on leasing costs, promote efficiency by consolidating far-flung offices and draw residents and tourists into the downtown area, he said.

The building is the "missing tooth in the otherwise beautiful smile of Pennsylvania Avenue," said Henry A. Berliner Jr., chairman of the Pennsylvania Avenue Development Corp. (PADC), which will handle the project.

The 50-year delay in finishing the huge complex of federal buildings lining Pennsylvania Avenue is "not from a lack of plans," said Jay Brodie, executive director of the corporation. It appears to have come to fruition now because of the combination of Moynihan, who pushed through the bill, Golden, who pushed through the financing method, and the Federal City Council, a local business group, which pushed through the concept of an international trade center to help revitalize the city.

PADC officials, too, played an important role in privately urging the administration early in the second term that it was "time to move before this president leaves office," Berliner said. He noted that the passage of such a major proposal through Congress by unanimous consent is almost unprecedented.

The trade center will be built under a relatively new federal building arrangement. The GSA will sign a 30-year master lease for the office space, which is used as collateral to obtain financing. A private developer, selected competitively, will construct the building and own it for the life of the lease. After that, it reverts to the government.

This "lease-to-own" arrangement, used by the federal government only four times in the past, is estimated to save the government $281 million over the 30-year lease, according to a report on the bill by the Senate Environmental and Public Works Committee.

GSA, which is the government's landlord, has estimated that a monumental, high-quality building can be built for $27 a foot, since the government already owns the property. Downtown office space would cost an estimated $35 a foot to lease from a private developer.

The center would be the second-largest federal building in the country. The largest is the Pentagon. It would contain roughly 1.4 million square feet for federal offices and 500,000 square feet for the trade center. By comparison, the Pengaton contains 3.8 million usable square feet.

The trade center is designed to house foreign missions, international state and local agencies concerned with trade and government-sponsored organizations supporting cultural exchanges. Ideally, city business leaders said, they hope the center will be full of international boutiques and restaurants.

GSA's eagerness for the project stems, in part, from its concern over skyrocketing rents. The government's current rental bill is $1.4 billion annually, up from about $400 million in 1970. Within the next 10 years, 95 percent of federal office leases will come up for renewal.

In the 1960s, the government stopped constructing buildings, according to the committee report, "partly over concern about annual spending. In the short run, it appeared less expensive to appropriate funds for an annual lease payment rather than to appropriate the entire cost of construction of a building up front."

The committee said it hoped the "lease to purchase" concept would be a model for future development. But the president's Office of Management and Budget has urged restraint in use of the technique, not wanting the government to commit itself to massive future expenditures without having the money available.

GSA also is eager to consolidate scattered offices. Golden testified that the project will help the Justice Department cut back on its locations from 38 to four.

The building site, a parking lot, is home to 1,300 cars and a small fountain. Moynihan's bill envisions that the new building will provide between 1,300 and 2,600 parking spaces. But providing underground parking along Pennsylvania Avenue can be difficult because the soil is marshy, Brodie said.

Another potential problem being studied is the security of a building designed to attract the public in an era of terrorist threats. "Starting from scratch on a development plan," said Kenneth Sparks, Federal City Council executive vice president, "the assumption is that it can be worked out."

The project, like any other federal project, still has many hoops to jump through before it can rise to the same height as the adjacent buildings on the avenue.

The president must appoint a 15-member International Cultural and Trade Center Commission to help develop the project and run the center. A development plan must be submitted for congressional approval. Plans must be approved by the National Capital Planning Commission and the Commission on Fine Arts, and the PADC must run a design and development competition.

The building is scheduled to be completed in "five years, maximum," Brodie said.

Model courtesy of Notter Finegold & Alexander Inc., Mariani & Associates, Bryant & Bryant