The U.S. visit of Pakistani Prime Minister Mohammed Khan Junejo, who is to arrive in Washington Tuesday to meet with President Reagan and other officials, will offer the 54-year-old Junejo a chance to boost his political standing as the government's day-to-day leader.

Junejo, who is managing Pakistan's evolution from martial law to parliamentary rule, is expected to discuss, among other issues, the U.N.-sponsored talks on a peace settlement in Afghanistan, U.S. support for the Afghan guerrilla forces, and narcotics trafficking, which has been a major irritant in U.S.-Pakistani relations.

The U.N.-sponsored talks in Geneva are scheduled to reopen at the end of this month and reportedly have been narrowed to the major question of a timetable for the withdrawal of Soviet troops and the method for monitoring that timetable.

In an interview before he left Islamabad for Turkey, West Germany and the United States, Junejo said the timetable is the only issue still under negotiation. But he stopped short of the usual insistence offered by Pakistani and U.S. officials on the withdrawal taking no more than six months.

At the last round of talks, Afghan officials reportedly laid out a proposed timetable of at least two years.

Junejo also said Islamabad favored humanitarian support for the Afghan guerrilla forces within Pakistan but not cross-border programs into Afghanistan.

The almost 3 million Afghan refugees in Pakistan have been a major administrative and financial problem for Islamabad as well as an increasing security risk as they become a target for attacks on Pakistani territory.

Terrorist bombings and cross-border shellings have become almost daily incidents in recent weeks, and Junejo appeared to be setting limits on the types of programs Pakistan will allow Washington to encourage and support among the Afghans.

More welcome will be his statements on the growing and trafficking of drugs.

Pakistan generally has cooperated with efforts to eradicate poppy growing in areas where the government's writ runs strong, but U.S. officials are known to be increasingly upset at what they consider inadequate attempts to curb trafficking amid an increase in this year's poppy crop.

Junejo said he has ordered that new laws be drafted to deal with the issue, promising that "all these people who engage in this business . . . should be dealt with seriously. There will be a rigid law, with heavy penalties."

The Pakistani leader was even more forceful in his criticism of the campaign by Benazir Bhutto, daughter of the late president Zulfiqar Ali Bhutto, to force new elections.

Bhutto returned to Pakistan in April to a tumultuous welcome and called for a new vote on a party basis to replace the parliament recently elected in a nonparty vote. Since then, she has been struggling to revitalize her People's Party and recently has signaled her intent to step up the level of confrontation against the regime of President Mohammed Zia ul-Haq, who ruled under martial law until last December.

Junejo's visit also comes at a time when the Reagan administration has requested that Pakistan, the fourth largest recipient of U.S. aid, receive a new six-year $4.2 billion aid package when the current $3.2 billion program ends in 1987.