Today, like every other day for the past 13 years, groups of people gathered on either side of the padlocked gates that seal the British colony of Gibraltar from Spain and yelled greetings and gossip to their separated relatives and friends across a 200 yard space of no man's land.

On this occasion, however, the bizarre rendezvous had an added poignancy. But for the Argentine invasion of the Falkland Islands, the rusty gates would have opened today and the divided communities of the British rock and the adjoining Spanish town of La Linea would have been united.

Following the Falklands invasion Spain and Britain prudently chose to shelve plans for talks at the foreign minister level on the future of Gibraltar scheduled for today in the Portuguese town of Sintra and for the simultaneous lifting of the blockade Gen. Francisco Franco imposed in 1969. A new date, June 25, has been set for the talks and the border opening, but La Linea's mayor, Juan Carmona, who actively seeks a negotiated solution to the dispute, echoed local feelings when he called the postponement "an intense disappointment."

In contrast a noisy, extreme right-wing demonstration in central Madrid last night took an aggressive line. Approximately 20,000 supporters of the Spanish Falange Party accused the government of selling out to London by planning to end Gibraltar restrictions, called on the Spanish Army to imitate Argentine generals and seize the rock by force and burned several British flags.

The slogan-chanting Francoists mirrored the intransigence of traditional "British we are, British we stay" opinion among Gibraltar's roughly 20,000 natives ever since Spain ceded the strategic peninsula at the western entrance to the Mediterranean to Britain in 1713.

Although Gibraltar has been claimed since by Spain as an integral part of its national territory, the issue came to a head during the Franco dictatorship when the blockade was imposed. "That was a complete mistake," said La Linea Mayor Carmona. "It drove the Gibraltarians further away from Spain and in the process it ruined us because La Linea's only reason to exist is that it is a frontier town with interchange and a customs house."

Even on the fiercely patriotic rock, the siege mentality appears to be lifting. The veteran chief minister, Sir Joshua Hassan, admitted that there was "a certain amount of disappointment" at the postponement. Traders, as in La Linea, had increased their stocks threefold in anticipation of the border opening.

According to Carmona, virtually everyone in La Linea has a relative in Gibraltar, where, in addition to English, Spanish is spoken with the thick southern accent of Andalusia.

Also, an official level reasonableness has replaced the antagonism of the Franco days. Diplomats focus on the possibilities for self-government for the Gibraltar community within the framework of Spain's quasi-federal democratic constitution. Spain's present negotiations to join the European Community and NATO explicitly involve a close working relationship with Britain and the possible future joint use of the Gibraltar naval base.

Both Madrid and London recognize that there is little point in holding talks over Gibraltar in the midst of the Falklands crisisA pointed riposte to the protesting Madrid rightists came from Carmona: "Franco himself said Gibraltar was not worth a war."