In the national celebration over the return of hostages from Iran, some Vietnam veterans expressed anger that their return from Southeast Asia had inspired little more than apathy or ostracism.

Hoping that history will treat them more kindly, a group of Vietnam veterans has been working for almost two years to insure that their efforts in battle will not be forgotten.

The Vietnam Veterans Memorial Fund plans to erect a "contemplative and reflective" monument in Constitution Gardens near the Lincoln Memorial. aThe Vietnam Veterans Memorial , expected to be completed within two years, will include the names of the 57,692 Americans who died in the Vietnam War and the 2,457 still missing.

An outpouring of interest in designing the memorial has produced one of the largest design competitions ever, according to the veterans group. More than 2,500 artists and architects across the country have paid $20 each to enter the contest, whose rules stipulate that the design be nonpolitical and not detract from the impact of the Lincoln Memorial.

The veterans group has been scrambling in recent weeks to find a warehouse large enough to hang thousands of 30-by-40-inch panels for the judges to review. Each competitor may enter two panel drawings.

A giant hangar at Andrews Air Force Base was offered to the veterans group last week, "after we had no response from newspaper ads to rent a warehouse here," said Jan Scruggs, the ex-Army infantryman who founded the memorial group two years ago.

The competition to design the memorial, expected to cost between $3 million and $5 million, is to be judged in April by a jury of eight nationally known architects and artists, who will take five days to reveiw the entires. The winning design will be announced May 4, and the whole hangar of designs will be open to the public May 9 and 10 during Armed Forces Day celebrations at Andrews.

The design competition alone will cost about $150,000, Scruggs said.Prizes of $20,000, $10,000 and $5,000 will be awarded the top three designs, in addition to as many as 15 honorable mentions at $1,000 each. The $50,000 in entry fees will thus cover only a third of the competition's cost.

The design requirements for the Vietnam memorial are somewhat similar of those for the only other memorial in the 5-year-old Constitution Gardens. That memorial, which will be dedicated to the 56 signers of the Declaration of Independence, was given final approval only last week by the National Capital Planning Commission. The cost of about $350,000 will be paid out of funds left over from the U.S. Bicentennial Commission. It will consist of 56 low stones surrounded by trees and shrubs and set in a semicircle on the small island in the Gardens' lake.

Constitution Gardens was developed during the Bicentennial to replace the World War I "Tempo" buildings erected on the edge of the Mall as temporary office space for the Navy Department. The dilapidated buildings were razed in the late 1960s.

The cost of the Vietnam Memorial, approved by Congress last year, will come entirely from donations. The Vietnam Veterans Memorial Fund already has raised about $850,000, most in response to more than 2 million direct-mail appeals sent out on Memorial and Veterans days last year.The organization now is concentrating on large gifts from corporations, foundations, and established veterans organizations, according to the fund's executive director, Robert W. Doubek.

The Sun Co. (Sunoco) last week gave the memorial its first major corporate contribution, $35,241 -- or $1 for each of its employes -- and has challenged the nation's two dozen major oil companies to do the same. The Sunoco gift was announced at a Washington luncheon for oil and gas company representatives, sponsored by Sunoco and the Independent Petroleum Association.

The IPA announced at the same time that the 7,000 small oil and gas producers it represents will in turn match any contributions made by the major oil companies.