With his rivals swept aside in the recent Kremlin housecleaning, Soviet leader Mikhail Gorbachev's next move is to convert the job of ceremonial president into an office of real power.

By next spring, if everything goes according to plan, President Gorbachev will be head of a more powerful and active Supreme Soviet, the legislature, while keeping his job as general secretary, the top officer of the ruling Soviet Communist Party.The forced retirement of President Andrei Gromyko in the Sept. 30-Oct. 1 bloodletting allowed Gorbachev to take over the office, whose authority is due to be pumped up through constitutional changes approved in July at the special 19th party conference.

That extraordinary meeting endorsed Gorbachev's proposal to shift much of the day-to-day management of national, provincial and local government away from the Communist Party to the soviets, or popularly elected councils, at the corresponding levels.

What is needed to speed up the lagging "perestroika," or restructuring, of the nation, Gorbachev told the conference last June 28, is a major overhaul of the political system capped by a new, powerful president.

Drafting of the changes is under way, according to Soviet publications, and the current Supreme Soviet is expected to consider the proposals this fall with the aim of putting the new system into effect with new national elections next spring.

Following Gorbachev's power blitz 10 days ago, he is unlikely to run into a rebuff, Soviet experts here say.

The new-style president would be head of a new national legislature, the Congress of the USSR People's Deputies, composed of 2,250 elected members, which would meet annually.

This congress would choose 400-450 of its members to form a bicameral Supreme Soviet to be a "supreme government body" passing laws and monitoring the performance of government ministries.

As head of the new Supreme Soviet, Gorbachev would be in effect the leader of both its houses. He will appoint the prime minister and be chairman of the national Defense Council, the core group of party, government and military policy-makers.

In American terms, Gorbachev's office would combine the powers of the president, the leader of the Senate and the speaker of the House.

The new president would be elected by secret ballot and could be recalled similarly. He would be "fully answerable and accountable to" the larger congress.

The new-style presidency, Gorbachev said, would have three benefits: enhancing the national system of elected councils, strengthening the rule of law, and "improving the representation of the Soviet Union in world affairs."

He cited the change as a return to the practice under Lenin, when the party leader was simultaneously the head of government. Since Lenin, some have, some haven't.

In practical terms, the Soviet public and the world would see more of Gorbachev in a governmental setting - speaking in the legislature and conferring with government ministers, for example - and less of him in his role as party boss.

Gorbachev, however, plans to retain his powerful positions in the party.