NATO foreign ministers today began to look beyond the forthcoming U.S. Soviet strategic arms limitation treaty to ways it might be used as a springboard for futher arms control initiatives.

Following a briefing by Secretary of State Cyrus Vance on the SALT II accord, the 15-nation alliance considered what U.S. source called "a lot of creative ideas about how to negotiate further arms limitations without impairing NATO's strength."

Essentially, these ideas involved moving from intercontinental missiles, covered by SALT II, to negotiating limits on the intermediate missiles and conventional forces, NATO and the Soviet-led Warsaw Pact have deployed against each other in Europe.

Various sources here stressed that all the ideas are preliminary and that the main goal at this annual meeting is, as one source said, "to try to sort them out and explore where we go next in the wake of the SALT agreement."

Vance came here knowing in advance that the SALT II treaty which is to be signed at Vienna next month, has the backing of almost all America's Western European allies.

The lone exception is France, which does not participate in NATO's collective military defenses but remains a member of the Atlantic Alliance and participates in many of its activities. Paris is concerned that the treaty could alter the strategic nuclear balance between the United States and the Soviet Union in ways that undercut France's independent nuclear force.

As a result, French Foreign Minister Jean Francois-Poncet today criticized as too high the ceilings imposed by the treaty on the number of missiles allowed to the two superpowers. The French criticism, however, was generally regarded as predictable and sources here said the main interest of most ministers focused not on second-guessing the treaty, but on talking about what comes next.

According to the sources, the principal discussion centered on what are known as theater nuclear forces - those using intermediate missiles based on the European mainland to strike European targets. The United States wants these missiles to become a major bargaining item in SALT III talkes with Moscow expected to begin after the SALT II treaty is approved.

Today, however, Vance and others argued strongly that NATO must seek to negotiate cuts in theater nuclear forces, while making a parallel effort to speed up modernization of its arsenal of intermediate-range missiles. They noted that the Soviet Union has undertaken several programs to improve its theater nuclear forces and said that if NATO is to negotiate successfully in this area, it must do so from a position of continued strength.

The other strategic issue undergoing extensive discussion here involves troop reduction talks that have been going on in Vienna between NATO and the Warsaw Pact for several years. The goal of these talks is to negotiate cuts in the troops and conventional weapons that the two sides have massed in Central Europe.

The talks so far have made almost no progress, and the West is starting to look for ways of breaking the deadlock.

The Warsaw Pact and France recently have made separate calls for a general European disarmament conference, and some NATO members are known to be interested in exploring whether it would be profitable to merge the Vienna talks with such a venture.

There also is discussion about whether the so-called "confidence-building measures" spelled out in the Helsinki accords on European security - such as advance notice of troop movements or maneuvers - could be applied to the Vienna talks to overcome disagreements about each side's respective troop strengths.

On another subject, the sources said that the Western powers with responsibility for West Berlin - the United States, Britain and France - recently conveyed a number of warnings to the Soviet Union not to cause trouble when elections are held in that city for representatives to the European Parliament.

The West contends that West Berlin, through its ties to West Germany, also is linked to the European Community and is entitled to participate in its affairs. That claim is disputed by the Soviet Union andEasy Germany. CAPTION: Picture, NATO dignitaries convene in The Hague yesterday for opening session of annual foreign minsters conference. UPI