U.S. Defense Secretary Harold Brown sought to assure Western European governments today that a new SALT treaty would not bar future NATO deployment of tactical cruise missiles.

Speaking at a news conference at the close of the semi-annual NATO defense ministers' meeting, Brown said the SALT II accord now taking shape would not prohibit continued development and testing of such weapons.

The cruise missile is basically a small, extremely accurate pilotless jet aircraft that is relatively inexpensive compared to piloted bombers or ballistic missiles.

The SALT negotiations between the United States and the Soviet Union are primarily concerned with placing limits on deployment of long-range strategic cruise missiles. America's NATO allies have recently become extremely concerned, however that restrictions would be placed on prospective future development of short-range cruise missiles as a battlefield weapon.

Western European governments view the tactical cruise missile as potentially a very low-cost way of offsetting the sizeable buildup of Soviet forces in Central Europe.

Today, both British and West German officials declared that they were reassured by Brown's explanations that the Americans would not give away European interests in these weapons prematurely.

Nevertheless, the subject is extremely complicated and many questions remain.

As things are shaping up, the emerging SALT II agreement would include a three-year protocol linked to a more permanent agreement that would run until 1985.

The principal American cruise missile that would be limited in the permanent agreement would be one launched from bombers and able to fly sufficiently far - perhaps 1,500 miles - to strike targets deep inside the Soviet Union.

All references to the short-range land or sea-based cruise missiles that the Europeans are interested in, however, are contained only in the protocol.

The protocol bans deployment of all cruise missiles with a range in excess of some 360 miles during this three-year period, Brown pointed out. "But this is no inhibition on what we or the allies could physically do," he said, because the missile would take some three years to develop anyway.

Cruise missiles can be developed and tested during this period, Brown said, and in addition, "the U.S. has made no commitment not to transfer cruise technology to its European allies."

At the end of the three-year protocol, Brown said, the U.S. and its allies will be in a position to weigh the pros and cons of cruise missile deployment.

Brown said he believed "it has been, and will be, possible for the United States to preserve the option for sea- and land-based cruise missiles for the alliance."

Europeans fear that in three years time, with the United States in another election campaign, there will be great domestic pressure to permanently ban cruise missiles.

In closed-door meetings here, officials said West German Defense Minister Georg Leber hammered away at Brown to insure that the United States would keep the option open on cruise missile deployment after the three-year period.

NATO Secretary-General Joseph Luns said he felt Brown had promised to make no concessions to the Soviet Union that would endanger Europe.Luns also said Brown pledged that if the United States wants to make concessions on the cruise missile, after the three-year period, it would do so only after full consultation with the allies.

The European interest in tactical cruise missiles is enormous. For West Germany, cruise missiles could be used against scores of targets instead of the new $20 million Tornado fighter-bomber now being developed.

On another controversial new weapon, the U.S. neutron warhead, Brown said the administration was now getting "feedback" from European leaders on the difficult political questions involved and that President Carter would consider this in deciding whether to proceed with deployment.

Several delegates said privately that a consensus had developed among NATO defense delegates that from a purely military standpoint, the weapon had advantages over existing nuclear warheads.

But the final decision, involving political as well as military considerations, was one for "presidents and chancellors," Brown said.

The final communique issued today also laid heavy emphasis on the "urgent need" for military assistance to Turkey and to a lesser extent, Portugal.

Leber, in particular, was sharply critical of the U.S. Congress for imposing a lingering arms embargo on a major NATO member along the weakened southern flank. He also gently chided Greece for seeking membership in the European Economic Community while staying out of the NATO military alliance.

The ministers also agreed on a revised concept for fielding a scaled-down force of some 18 U.S.-developed airborne early warning planes, known as AWACS, which would work in conjunction with a British plane called Nimrod. The new plan, however, deals only with research and development at this point.