A Senate-House conference committee agreed yesterday not to penalize Pakistan for illegally seeking to import U.S. nuclear materials, hours before a federal jury in Philadelphia convicted a Pakistani native of that offense.

The action by conferees on the catchall continuing appropriations bill grants Pakistan a 2 1/2-year waiver from U.S. nuclear nonproliferation laws and provides $260 million in foreign military sales assistance and $220 million in economic assistance for the fiscal year ending Sept. 30.

There had been moves in Congress to cut off or severely restrict Pakistani aid because of continuing reports that it is developing a nuclear weapons program and especially after the arrest in mid-July of Arshad Z. Pervez, a Canadian citizen of Pakistani origin, on charges of seeking to illegally provide Pakistan with sensitive U.S. materials used in making atomic weapons.

The drive in Congress for sanctions against Pakistan on antiproliferation grounds was countered and eventually overwhelmed by the congressional determination to continue supporting Pakistan because of its role in assisting the anti-Soviet resistance in neighboring Afghanistan, and because of its vulnerability to Soviet pressures.

Rep. Stephen J. Solarz (D-N.Y.), a key figure on the Pakistan issue in the House, said earlier that it was a classic congressional struggle between competing objectives: "whether we attach more importance to our nuclear nonproliferation objectives or to support of our Afghanistan policies."

Solarz said the issue may not have been resolved by yesterday's conference committee vote, in view of Pervez's conviction later in the day. This is because of a 1985 measure, bearing Solarz's name, which mandates a cutoff of U.S. aid if a nonnuclear weapons country such as Pakistan attempts to illegally import nuclear weapons material from the United States.

"The president has an affirmative responsibility to carry out the law, and the law requires a termination of aid," said Solarz. Particularly after the conviction of Pervez in a U.S. court, "the president has a legal and moral responsibility to act," he said.

Pervez was found guilty of conspiring to defraud the U.S. government and of making false statements in applying for a license to export to Pakistan maraging 350 steel, a rare alloy used almost exclusively in uranium processing. Its export is tightly controlled by the U.S. government. The jury acquitted Pervez of a related charge of bribery.

Assistant U.S. Attorney Amy Kurland, who prosecuted the case, said "this verdict shows the jury believes there was a conspiracy here to defraud the government, and that these materials were intended for Pakistan's nuclear program," United Press International reported from Philadelphia.

Pervez could be sentenced to up to 25 years in prison and fined $1 million. Sentencing is scheduled for Feb. 10.