The United States is expediting delivery of Sidewinder and Stinger missiles to Pakistan as part of its effort to bolster defenses there against increasing Soviet and Afghan air incursions, the State Department said yesterday.

A State Department statement said "a number" of AIM9L air-to-air missiles, known as Sidewinders, previously on order for Pakistan's fleet of U.S.-provided F16 fighters, was being shipped "as well as other appropriate air-defense equipment" to enhance that country's ability to deal with the threat to its western border.

The statement said explicitly that the decision to expedite the shipment was "in response to repeated violations of Pakistan's airspace and territory by communist aircraft operating from Afghanistan," and called the missiles "an appropriate response" to them.

No other details were made public. But U.S officials said that 100 Sidewinders are being rushed to Pakistan and that the "other appropriate air-defense equipment" involves an unspecified number of shoulder-fired, surface-to-air Stinger missiles worth $8.5 million.

A Pakistani request for ground or airborne radar for improved detection and interception of Afghan aircraft on quick incursions remains under study, one official said.

The increasing air incursions, some reportedly by Soviet-piloted planes, has been interpreted as indicating a Soviet attempt to increase pressure on the Pakistani government to curtail support for Afghan rebels fighting the Soviet-backed communist government in Kabul.

Last March 5, the administration formally notified Congress of its intent to provide Pakistan with a $50 million package of air-defense equipment, including 500 Sidewinders, support equipment and technical training on the missiles.

The 100 Sidewinders being rushed there are part of this package, but the Stingers are an extra, a U.S. official said.

The United States has earmarked $325 million for military assistance to Pakistan this fiscal year on a "market rate financing" basis, which means it must pay interest at the going market rates. This has placed financial constraints on what Pakistanis can afford to buy for defense in addition to 40 F16s already purchased.

The United States is also providing $200 million in economic support to Pakistan this year.

The administration announced in early March its intention to sell a more modern version of the Sidewinder, which the United States has been supplying to Pakistan since the 1960s.

Michael H. Armacost, undersecretary of state for political affairs, during a trip to Pakistan later that month made clear the administration's concern about increased across-the-border air raids and ground attacks from Afghanistan.

"We recognize the pressures imposed on Pakistan by the Soviet occupation with 100,000 troops in Afghanistan," he told reporters in Islamabad. "It is for this reason that we offered the kind of military assistance that would augment the air-defense capabilities of Pakistan."

More raids have occurred since then and, on June 9, Pakistani President Mohammed Zia ul-Haq formally accused Soviet pilots for the first time of taking part.

At the time, Reuter news agency quoted a senior Pakistani Foreign Ministry official as saying Pakistan had tried but failed to shoot down intruding aircraft.

Pakistan faces a particularly difficult task in intercepting Afghan planes because its western border area is extremely mountainous with few radar facilities to provide the kind of warning necessary for quick response.

Last October, Pakistan asked the United States about purchasing Grumman Hawkeye E2C aircraft for early-warning border surveillance. No decision has been made on that request, and a U.S. official suggested that it might be easier and less expensive for Pakistan to install radar in its U.S.-provided C130 transport planes.