By Steve Holland

WASHINGTON, March 6 (Reuters) - U.S. President Donald Trump said on Thursday he likely will make his first trip abroad to Saudi Arabia to seal an agreement for Riyadh to invest upwards of $1 trillion in the U.S. economy, including purchases of military equipment.

Talking to reporters in the Oval Office, Trump said he would probably travel there in the next month and a half. He noted that the first overseas trip of his first term was to Riyadh in 2017 to announce Saudi investments estimated then to be worth $350 billion.

"This time, they've gotten richer, we've all gotten older," said Trump.He said that, at his behest, the Saudis were willing to invest $1 trillion over four years in American companies including purchases of U.S. military equipment.

"And they've agreed to do that, so I'm going to be going there, and I have a great relationship with them, and they've been very nice," Trump said.

Saudi Arabia has been taking a more prominent role in U.S. foreign policy. Trump's Middle East special envoy Steve Witkoff told reporters the Saudis will host a U.S.-Ukraine meeting next week to discuss a ceasefire in the Ukraine war.

In February, Trump met with officials of the PGA Tour and the Saudi-owned LIV Golf about resolving a rift between the two.

Jared Kushner, the president's son-in-law and Middle East adviser during his first term, started a private equity firm that received $2 billion in Saudi investment after Trump left office.

Trump has also recently presided over a string of announcements about companies investing heavily in the U.S. economy including Taiwan Semiconductor Manufacturing 2330.TW and Apple AAPL.O.

(Reporting by Steve Holland, Katharine Jackson and Doina Chiacu; Editing by Cynthia Osterman)

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