The Reagan administration is learning a familiar Washington lesson: trade policy often clashes with foreign policy.
The administration is scrambling to square its harsh anti-Soviet rhetoric with its continued grain sales to Moscow and its private assurances that the US won't block the Soviet pipeline to supply natural gas to Western Europe.
Republican congressmen in the Midwest want trade agreements kept. Their states export the grain and heavy equipment for the pipeline that the Soviets need.
Short term, they worry that trade disruptions will worsen the recession. Long term, says a congressional insider, the concern is that while most countries ''hold international contracts sacred, the US is gaining a reputation for breaking trade agreements.''