Kurdish insurgents trying to carve out an autonomous region in Iraq are claiming their most important victory in 25 years in fighting that threatens the already hard-pressed Iraqi government with closure of a vital international highway and oil pipeline near the Turkish border.

Masud Barzani, son of Mustafa Barzani, who led three major revolts against Iraq before his death in 1979, made the victory claim in a recent interview in Damascus. Barzani is the 39-year-old leader of the Kurdish Democratic Party.

The reported fighting would indicate that Barzani's forces, backed by Libya and especially Iran, were stepping up operations in the north of Iraq as part of a strategy to draw Iraqi troops away from the southern and central fronts where they face major concentrations of Iranian troops in the now almost six-year-old Iran-Iraq war.

Barzani claimed that 1,500 Iraqi troops and large amounts of equipment had been captured in heavy weekend fighting around the mountain town of Mangesh, less than 30 miles from the Turkish border and even closer to a busy highway that links Turkey with the northern oil center of Mosul and with Baghdad, the Iraqi capital.

Reports on the fighting have been carried by the Reuter news agency, reporting out of Iran, and by the British Broadcasting Corp., although the Iraqi government has thus far said nothing about the clashes.

In Washington, State Department officials said they had not heard reports of fighting in the area around Mangesh.

The Iraqi oil pipeline crossing Turkey to the Mediterranean runs parallel to the highway, which enters Turkey near the border with Syria. Until completion of another pipeline through Saudi Arabia last year, this route was Iraq's sole means of exporting its only significant earner of foreign exchange.

Indicative of the high stakes involved in Mangesh, Barzani said, was Iraq's decision to commit its strategic reserve, the Presidential Guards. But Barzani said the guards were making "no headway" despite their use of fighter-bombers and helicopter gunships.

The guards were rushed in when an Army battalion, backed by the lightly armed People's Militia, collapsed, apparently as a result of the defection of forcibly conscripted Kurdish troops, according to Barzani.

The guards suffered heavy casualties when last deployed in February. That was in the early stages of Iraq's still unsuccessful effort to retake the Iranian-held port of Faw, the prewar Iraqi oil exporting center at the mouth of the Shatt al Arab leading to the Persian Gulf.

Captured in the current fighting "for the first time" were intact tanks as well as armored cars, antiaircraft weapons, artillery, mortars and great quantities of ammunition, according to Barzani, who said the victory provided "a shot in the arm for our morale."

Earlier reports said that Libya had provided Barzani with long-range artillery, which was delivered through Iran.

Barzani said that even before the Mangesh fighting, his forces had cut the international road a half dozen times this spring.

But he also recalled that in May 1983, Turkish troops entered two to three miles into northern Iraq and stayed there for five days. That incursion was made under an agreement between Ankara and Baghdad, still in effect, that authorizes both nations' forces to operate up to 18 miles inside each other's territory.

Those remarks apparently reflected fears that Iraq and Turkey might again cooperate -- perhaps in a longer-term, more massive fashion -- if the Kurds' troops sought to interrupt the vital truck supply route, much less cut the pipeline on anything like a permanent basis.

Barzani credited the local Kurdish population and Kurdish Democratic Party militants, joined by defectors from Kurdish units of the Iraqi Army, with forcing the surrender of the first 800 Iraqi soldiers in the early stages of the Mangesh fighting, which began May 14.

Barzani compared the current fighting to the battle of Mt. Hindarain, southeast of Rowanduz near the Iranian border, in which his father's forces wiped out the Iraqi 4th Brigade in 1966.

Kurdish uprisings in this century have centered on Iran, where 5 million Kurds live, and Iraq, with a Kurdish population of 3.5 million.