A restructuring of U.S. military forces to give them more clout in the Third World and higher military spending for the foreseeable future will come in response to the Iranian crisis, a wide spectrum of senators predicted yesterday.

The post-Vietnam tunnel vision that resulted in the Pentagon concentrating on building up NATO has been widened, they said, because of what Sen. Henry M. Jackson (D-Wash.) called "the geopolitics of the oil barrel."

The Iranian crisis, Jackson said, has forced policy-makers and the public to confront the fact that "the Middle East is unique" because when something goes wrong there it can have both military and economic consequences.

Generals and admirals asking Congress for money next year, several senators predicted, will be questioned how their forces could protect U.S. interests in the Middle East as well as reassure such friends there as Saudi Arabia and Egypt.

Also, in contrast to the congressional resistance of four years ago, almost anything the Pentagon wanted to do in the Indian Ocean and its tiny island of Diego Garcia will receive a sympatheitc hearing, according to influentional lawmakers.

With the Sovient Union using the former British port of Aden on the Gulf of Aden adjacent to the Indian Ocean, Jackson said, "there is no way" the United States can stay out of the Indian Ocean. Currently, the U.S. Navy stores fuel for warships and has an airstrip on the British-owned island of Diego Garcia.

Defense Secretary Harold Brown already has started to restructure the armed services to make them more responsive to Third World problems. His blueprint includes spending $9 billion over the next five years for new long-range planes to carry troops to distant trouble spots and a fleet of cargo ships full of military gear anchored in easy reach of Third World countries.

This gearing up for an intervention capability may be challenged in some quarters as a return to the world policeman role of the 1960s. But senators interviewed yesterday predicted that the series of events in the Third World, ranging from Cuban troops in Angola to the latest turmoil in Iran, would overwhelm such challenges in Congress.

Sen. John Stennis (D-Miss.), chairman of the Senate Armed Services Committee and of the defense appropriations subcommittee said, "I never thought" it would be the little countries that would challenge the power of the United States in the 1970s.

While the United States must continue to keep up its guard strategically, stennis said, "We have more problems than just strategic threats. We've got to be prepared for more uncertainties" and build forces "that can go into the bayous" of the Third World.

This means, Stennis said, that the United States should build lighter and cheaper weapons instead of more super ships like the $2 billion Nimitz aircraft carrier.

Sen. Gary Hart (D-Colo.) a memberof Stennis' committee, agree, declaring that Iran has "underscored dramatically the need for flexibility, mobility and presence."

Hart said, "The only way you accomplish those three goals is through a greater maritime strategy. The United Stated must disperse its assests at sea instead of continuing to concentrate them in a few carrier task forces." a

Iran has shown, Hart continued, thatthe United States "cannot be entranced with Europe, NATO. More and more of the burden of defending NATO on land should be assumed by the allies" while the United States deploys air and sea power to keep supply lines open.

Hart has been at the forefront of those senators pushing for smaller aircraft carriers and other highly mobile forces to project U.S. power in remote corners of the world. He said he will continue to press for restructuring U.S. forces, and said the climate to do that has been improved by developments in Iran.

"We should be able to do a lot of different things on very short notice" militarily, Hart said. "it shouldn't take us 10 days" to send an aircraft carrier from the Pacific to the Indian Ocean to provide an American military presence off Iran, as was the case with the Kitty Hawk sent there recently.

Sen. William L. Armstrong (R-Colo.) agreed that the Iranian crisis has forced the Congress to reassess the military forces. But he disagreed with Hart by declaring the Navy should keep building big carriers like the Nimitz because "when you need a carrier, something else is not a substitute."

Armstrong reflected the prevailing view both in the Pentagon and in Congress by declaring the U.S. airlift "obviously terrible."

Senators across the political spectrum seem to agree that higher defense budgets will be demanded in Congress for the foreseeable future because of the events stretching from Angola to Soviet troops in Cuba to Iran.

Sen. Bob Dole of Kansas, a conservative running for the Republican presidential nomination said "the fallout from Iran is going to be more defense spending" even though more forces could not have rescued the American hostages in Tehran.

Sen. William Proxmire (D-Wis.), who has been at the opposite end of the political spectrum from Dole in fighting off higher defense spending, agreed the immediate fallout from Iran will be more money for the military.

"It's mindless to increase the defense budget by a fixed percent every year without justifying it," Proxmire complained. But he agreed this is happening because "of emotion and frustration" over challenges to the United States in the Third World.